The most valuable thing for me is my photo library. All of them are currently in Google Photos. Is there any easy way to backup just that? I don’t care about my personal email, tasks, calendar etc. It’s just the thought of losing my photos scares me.

There's a decent guide here: https://ubuntu.com/blog/safely-backup-google-photos.

I run this every night on a raspberry pi, syncing them to my local NAS which is in turn backed up to cloud storage.