Snapshot management

Hey everyone,

on my FreedomBox there is a folder “.snapshots” in the root directory which is claiming huge amounts of disk space and I have no idea how to handle the snapshots inside.
I’ve already deleted every system snapshot in plinth. Deleting the directory via terminal doesn’t work, because it is read-only (chmod doesn’t work as well).

Can anybody tell me where these snapshots come from and how to handle them?

Seems to have something to do with btrfs, because there is an subvolume-entry in the fstab…