ok, managed to fix mine by following fastboot flashing instructions from here: https://support.fairphone.com/hc/en-us/articles/360048050332 with the exception of not unlocking the bootloader the standard way. i unlocked the bootloader before applying the instructions and relocked it afterwards with these instructions..
haven’t lost any data. \o/
now to quickly backup everything ^^;
@unclelutz i hope this helps you and i am not too late.