Hello,
Are you working with BTRFS?
If yes, you should remove the read only property of the BTRFS snapshots to allow remove them (or change their permissions).
From the shell you should run the command: “btrfs property set -ts /backupsfolder/computer/date ro false”
/backupsfolder/computer/date → change with yours.
You should do this for each backup and then you can delete or change their permissions.