This morning I noticed that my home PC is loading 5 out of 20 cores without
running application software.
In htop I found that the only consumer of CPU time is snapperd.
The same lines appear in the /var/log/snapper.log file several times a second:
> 2024-04-05 08:57:46 WAR libsnapper(1375) BtrfsUtils.cc(quota_rescan):474 - waiting for old quota rescan to finish
> 2024-04-05 08:57:46 WAR libsnapper(1375) BtrfsUtils.cc(quota_rescan):474 - waiting for old quota rescan to finish
> 2024-04-05 08:57:46 WAR libsnapper(1375) BtrfsUtils.cc(quota_rescan):474 - waiting for old quota rescan to finish

I tried:
> [werwolf@home] ~  
> ❯ sudo btrfs quota disable / && sudo systemctl restart snapperd

the CPU load ended, but after a couple of hours I again found exactly the same
behavior with the same messages in the log.