@movq@www.uninformativ.de Pretty much. In my situation I was able to delete some files and snapshots and run a couple of different btrfs balance commands to move some allocations around. It looked like writes weren’t all committed properly to the disk but nothing told me that explicitly.
I did a system update in this state and I think I remember mkinitcpio throwing more warnings than usual but I was doing something else and I didn’t pay close attention to them. This coincided with a power outage and there was a lot of inconsistency, making me think it was hardware related. It was just btrfs, as far as I can tell, and I fixed it by reinstalling all the packages on the system once there was enough room. Luckily, I hadn’t done anything important with that computer after the system update.