¿Why you want to "downgrade" Windows 10 to Win8.1 in 2022? instead of "upgrading" to Windows 11? & How to do it...
A bit of History:
Long ago, in the WinXp era, Vista era, W7 era, computers that came with Windows pre-installed from factory, built by Authorized "Partners", like HP, Compaq, Acer, Gateway, etc...
came with a Windows Sticker called COA Certificate Of Authenticity that included the Windows Activation Key, but... that sticker gets damaged very easy, usually was on the bottom of the Laptop, where the heat and scratches damage the sticker.
to solve that problem: New computers, manufactured and sold in 2006 or later that came with Windows 8 pre-installed, had Windows Activation key stored in the Bios / UEFI of the computer. No more stickers.
The Hardware is the Key, and thats very good.
the problem is that those computers used a "special" version of Windows, and the problem with Windows is that, if you do Not install the same compatible version, Activation key does Not work... Even if the key is legit and valid, does Not Activate. A valid Windows8.1 key does Not activate Windows8.1 IF the installer CD/DVD does Not match the version. that happens since WinXP. Microsoft created many different installers for the same Operating system.
Windows is Not designed or smart to Activate Windows with a valid Key, and change features acording to the Key level.
you need to download a completely different installer, erase everything and install again. Example: if you download Windows 8.1 Standard, or Single Language or K or N, or KN.
legit Windows Activation key stored in most UEFI/Bios will Not work. but is "the same" Windows. call it paranoia. you need to find a special Recovery DVD installer, was $55usd.. Discontinued long ago, and No longer sold. also buy an external USB DVD drive for computers without DVD, like HP Stream 7 tablet.
That "special" Windows is called: RTM Core / Bing Edition, Not downloadable from Windows Website, Nor any other Authorized "Partner". the reason: anti-monopoly law makes illegal to include Bing as default Search engine in Windows.
Microsoft had several Law suits and lost. Thats why the "special" Windows version cannot be downloaded from Microsoft website.
if you upgraded W8.1 to free W10 update and didnt like it, wanted to rollback and re-install Windows 8.1 later, but your HDD was small, usually the Rollback partition was deleted because it was imposible to use W10, Now can´t re-install Win8.1 with standard official iso installers.
Option A) buy another Windows license if you want to use standard windows installer. Pay for something you already have paid. Worse option, but has some advantages. Full Retail Licence allows multiple languages, and is Not Hardware locked. you can create a restore back-up and move Windows to another Hardware. HP Tablet does Not allow to remove ssd drive.
Option B) create your own RTM Core Windows Bing installer DVD with DISM.exe there are tutorials in Microsoft website for Developers, for Deploy especialists. Complicated. https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-8.1-and-8/dn613856(v=win.10)
Option C) Download the discontinued Restore DVD image from torrent or way back machine archive do a Clean install. delete large partition and recovery partition, Not smaller boot partitions. Recovery partition is almost never used, not required, and small ssd/hdd need that space for virtual ram more.
Option D) Download a pre-installed Restore Image, install from a Windows restore USB. Saves time downloading updates.
In my opinion C) is the "standard" way to do a clean install. Windows RTM core Bing will detect Activation keys stored in the Bios / UEFI and Activate Automatically when connected to internet. No need to type keys, like standard version. but DVD image is Old, and requires long hours of Updates, Windows8.1 has been improved a lot over the years, for examplre: to include Edge Browser. recomended to buy a USB2.0 to Ethernet adapter, there are many brands that do Not require drivers, like Belkin F4U047, except Apple USB Ethernet adapter "same chip" but requires Bootcamp5 asix driver ax88772c, different HW ID, easy to find, or download driver from Asix.com.tw website.
Better and faster than Wi-Fi. https://en.wikipedia.org/wiki/Boot_Camp_(software)#Boot_Camp_support_software_(for_Windows)_version_history
after install & update, configure Windows8.1 to taste, install Browsers: browser.yandex.com Opera.com Mozilla Firefox Vivaldi Brave Chrome / Chromium Telegram / WhatsApp Desktop, Oracle OpenOffice / MS Office, etc...
set All to Dark mode, Disable Automatic updates in msconfig for Browsers. disable most startup items in TaskManager. because old hardware is very limited: RAM, CPU, SSD. also Disable "BitLocker" ssd/hdd Encryption. in Weak Hardware to preserve CPU, RAM & Battery. drive cannot be removed anyway. and you should never put confidential info in C: drive in a mobile device anyway. Disable Encryption At Your Own Risk. at the New Configuration Menu, Not with Control Panel.
create a Restore Back-up image on a external HDD, Done.
Clean install = 1 day of work to install & update Windows8.1 IF you have all tools required: OTG cable, USB memory, Battery fully charged, USB Hub, etc...
Option D) the most desireable, because long updates of clean install, you only need to do option C) once, then create a Restore image .vhdx in Windows / Control Panel / System and Security / File History / System Image Backup / Create a system image. also Create a Recovery USB drive.
and Install / restore that image to other machines or same machine later if want a Clean install again...
needs a software to read the Bios/UEFI Activation Keys if installing to other machine, and Change manually Windows Key to the Actual Key stored in the other UEFI machine.
If Windows detects 2 machines online with same Key, will Deactivate both. there are many softwares available to read the keys stored in the UEFI Bios. if machine was pre-installed with Windows8 from factory, 2006 or newer.
¿why Not install Win11 instead? W11 is designed for newer computers, minimum requirements are high. unless you modify the installer.
W11 has Dark mode, and some improvements over W10 but Not over W8.1
W10 was inferior to W8.1 W8.1 was ahead of its time. W11 still is Not there yet.
W11 vs. W10 is like: OSX Mojave vs. OSX Catalina. or OSX Sierra vs. OSX High Sierra, "almost the same"
in my opinion going back to W8.1 is going back to the future.
better in anyway than W10.
some games & machines does Not work in W8.1 but are rare, a small minority, most will.
you need to download HP Stream 7 drivers for Win8.1 https://support.hp.com/us-en/drivers/selfservice/hp-stream-tablets/7439994/model/7482041
some people think: Windows 8.1 RTM Core "Bing" Edition is an inferior, cutdown version of standard Win8.1 Single Languaje.
in my experience, seems more advanced, smarter in some ways. for example: Auto detecting the Activation keys in the UEFI/Bios. Teaching how to use the Tablet mode in real time, on the run, not with a boring Skip tutorial. etc... thats the advantage of a Clean W8.1 install, the tutorial, very good.
if want to go back to W10 for some strange reason, you can make a Restore image BEFORE Deleting the SSD / HDD, W10 will return to exactly the same condition you left.
There is No Risk installing W8.1 IF you make Image Bakcups. only need a large 1TB external USB3.0 drive, formatted in NTFS to store the image backup. and also to have multiple Images stored in different folder: W8.1 W10, W11.
To me W10 is inferior, Pointless to make a back-up, but thats just my opinion.
2014 RTM Core Bing Editions:
magnet:?xt=urn:btih:cc9748e655915fbe107ca6196cebda51d544a108&dn=X19-57134_SW_DVD9_NTRL_Win_with_Bing_8.1_32BIT_English_OEM.img
magnet:?xt=urn:btih:af8ffdaae70636719b0d70f1d30f1ba5359710b8&dn=X19-57272_SW_DVD9_NTRL_Win_with_Bing_8.1_64BIT_English_OEM.img
https://archive.org/details/Windows8.1WithBing
https://archive.org/download/Windows8.1WithBing/Windows8.1WithBing_archive.torrent
download Rufus to create a USB installer. https://rufus.ie/en/ or any other, there are others, Unebootin, USB Pen Drive, Ubuntu disks, etc...
HP Stream 7 was 32-Bit, unknown if 64-Bit version will install. if older Bios will detect 64-Bit USB installer.
with 32-Bit version, you need to install a fast microSD 32GB U3 card inside HP Stream7. format NTFS, create a large pagefile.sys Virtual Memory in D: 4000MB minimum, 4092MB max. same for C: drive. will overcome the 1GB of RAM limitation. the faster the microSD, the better.
Software to see UEFI Windows Activation Key: https://h30434.www3.hp.com/psg/attachments/psg/OS/539223/2/ShowKeyPlus1.0.6477.zip works with HP Stream 7, may Not work with other brands of computers. Not needed with RTM Core Bing Edition. But is nice to known the Activation keys in your Bios before making a Bios upgrade. to latest .0F
i recomend storing the Bios file in a USB drive, and upgrade Bios when booting pressing Power Button 1 second + Holding Volume Down. F1 or F2 Bios option. All upgrades must be done with battery full, over 95%.
Windows8.1 Standard & Single Language Downloads: https://www.microsoft.com/en-us/software-download/windows8ISO Not needed with computers from 2006 with pre-installed Windows8 from factory.
Emergency Generic Activation key for W8.1 standard. 334NH-RXG76-64THK-C7CKG-D3VPT To install without a Key, Will Not activate Windows, only allows to install Win8.1 then use a software to read the key stored in the bios, OR... find the key card included in the boxed Windows "retail version", or... the email key when puchased from microsoft store.
manually type the Activation key when connected to internet.
If you purchased a Boxed Windows8/8.1, OEM, Full Retail or Virtual License from Microsoft online store. you have a Key Card with the Activation Code.
if you lost the key card, you need to buy another key again from windows, if key is Not stored in the UEFI / Bios. BUt... Microsoft does Not sell 8.1 licenses, and W10 OEM license does Not allow to Downgrade to 8.1, only Pro & Enterprice licenses allow to Downgrade. OEM licenses are Not interchangeable between different Hardware. Cannot be ReActivated in a different Hardware. OEM are Hardware locked. If Hardware fails, license is lost. if you have a System Image Backup, you can restore Windows to another machine, new hdd, if its a Pro or Enterprise Full Licesnse. OEM allow to make System Backup & Restore to same machine.
Retail, Boxed, Full Online Store license "Not OEM, Not Single Language, Not N, Not K" can be ReActivated unlimited times in different Hardwares.
Other alternative: if want to go Back to XP, NT4 era. try: https://reactos.org/
Donationware, code compatible, drivers compatible, based on Wine. usually for old software using Parallel Port devices, like CNC machines.
Windows does Not sell XP license anymore, New activation key does Not allow to "Downgrade/Activate" XP.
Only 2 generations lower. W11 license allows to downgrade to W10, and Win8.1 W10 license allows to downgrade to W8.1 and W7. W8.1 license allows to downgrade to W7, and Vista. W7 license allows to downgrade to Vista, and XP.
P.D. HP Stream 7 Tablet requires a microUSB OTG cable... i recomend Dell XGJT2, that has 2 female Usb, micro and standard. a 2A microUSB charger with FAT cable... cheap small thin cables will fail in 1 month. Charge will become slower. a Powered USB 2.0 Hub, Belkin brand with No led, and swtiches is recommended. there are more advanced OTG docks with HDMI output, but more $$.
what is the HP Stream useful for? many solar charge controllers have USB to serial emulator, + controller software. others have Wi-Fi optional modules... also some DMX light controllers, have a USB to DMX, and controllers Software... all those applications are easy to do on a HP Stream7 Tablet, even with limited 768p resolution.
this is the cheapest computer you can buy, will work well for many office type tasks, No 3d gaming.
Win8.1 Dark Theme: simple way to have Semi-Hollow Dark Theme, Mouse Right Click in Empty Desktop, Personalize, set Wallpaper to Solid Color, and Select Black. RGB0,0,0
Download: WinaeroTweaker https://winaero.com/winaero-tweaker/#download
set: Appereance: Aero Colors: Aero Color [Black], Color Balance 100, Apply & Save. Then: Advanced Appereance Settings: Window Borders: Custom Window Borders: Border width: 1 Border padding: 0 Apply
Will Giove a Hollow Dark Slim Modern Look.