After losing my build.prop (and trying various things while troubleshooting), I tried dirty flashing the latest AOSIP update - which failed.
There was no more fastbootD, no recovery, and neither 'fastboot boot twrp.img' worked anymore (I was stuck at the bootloader).
However, I changed active slot with fastboot and now I have again recovery and fastbootD and can boot twrp again.
Now I'm really worried about messing again, and I would be super grateful for any help.
This was the error:
fastboot reboot fastboot
fastboot update OSiP-10-Gapps-hotdogb-20210621-img.zip
--------------------------------------------
Bootloader Version...: unknown
Baseband Version.....:
Serial Number........: 9de0f5c0
--------------------------------------------
extracting android-info.txt (0 MB) to RAM...
android-info.txt syntax error:
Setting current slot to 'b'
FAILED (remote: 'set_active command is not allowed on locked devices')
Should I dirty update from TWRP instead of from fastbootD?
Which *SLOT* do I update from/to?