This UWP app opens YouTube third party apps when the user click on a YouTube link using Windows 10 (Mobile)'s Apps for websites functionality.

You can choose from a dropdown menu which app you want to open or you can also provide a custom URI scheme to open your preferred app if it's not already in the list.

Unfortunately it works only if it's sideloaded, apps installed from the Microsoft Store require a file on the root of the website to work.