Description

After having flashed BOARD=feather-nrf52840-sense at least once with RIOT, I was no longer able to install CircuitPython on it. For a new and untouched board of the same type it works as described on https://learn.adafruit.com/adafruit-feather-sense/circuitpython-on-feather-sense

Also reproduced with BOARD=seeedstudio-xiao-nrf52840 from #20980.

Steps to reproduce the issue

1. Take a board using the UF2 bootloader, e.g. BOARD=feather-nrf52840-sense.
2. Flash some RIOT application on it (e.g., make -C examples/hello-world flash)
3. Try to flash the UF2 file from https://circuitpython.org/board/feather_bluefruit_sense/ by copying it to the USB device from bootloader mode
4. See no error, but notice that CIRCUITPY does not appear.
5. Also see, that the serial connection via make term still shows the RIOT greeting.

Expected results

CircuitPython starts and can be used as expected.

Actual results

RIOT still remains on the board.

Versions

tested with current RIOT master, but also happened with boards previously running some older version of RIOT