Just to confirm here:
- I just transfered my data to my new phone and
- (as @hirnsushi suggested - thx again) re-flashed CalyxOS with the device flasher → just following the normal install description: Install on Fairphone 4
- I also locked the bootloader this time (more save for the un-expierienced Family member) - I was a bit unsure and then the device flasher stopped already so I did it via:
fastboot flashing get_unlock_ability
I got → (bootloader) get_unlock_ability: 1- and finally locked it via
fastboot flashing lock
- transferring the data (from the FP2 to the FP4) will probably be done via USB cable most (the messenger like WhatsApp and Signal have a nice Transfer to new Device functionality via WiFi - contacts are at google in their case anyway )