Cmk folder permissions docker

What is up with the strange permissions for the checkmk/cmk site folder? I am running rootless docker so I can have more security and easier backups, and all the files in the site folder are owned by 1009999:100999 and not the user it is running as.

What is strange here?

The site folder files belong to the site user and not to the user the container runs as.
That is the same also for installations outside docker.

It makes backups problematic.

drwxr-x–x 8 100999 100999 4096 Dec 4 00:52 cmk

This user and group doesn’t even exist on the host system but it makes it so restic fails to back it up without root permission.