Fairphone 4 - stuck on recovery screen - need instructions for further action

so I tried to send the command from the Mac via terminal to the USB-connected phone, but unfortunately got an error message:
fastboot --set-active=b
Setting current slot to ‘b’ FAILED (remote: ‘set_active command is not allowed on locked devices’)
fastboot: error: Command failed

My research showed that when I unlock the bootloader with adb, the phone does a factory reset. This is actually not desired on my part. How can I proceed without losing data/settings?

Also, to understand the problem (and what i propably did wrong) - why switched the phone to slot b?

Alternative:
How can i copy at least my photos and videos to my mac using adb? I found the pull command, but i cant find any folder with my photos. i assume ls -R / will show only files and folders from slot b, but not from slot a where the photos should be?