it would be great if the backup can be chosen as:
1 - system and userdata backup (as now)
LibreELEC's internal Backup/Restore tool has never included system files, only the most part of the /storage partition.
The system files are on a read-only partition, so if changes were to be made, you would need to unlock that part first.
I'd go for 2 backups:
- all files in storage via a sync command, so incremental backups can be made (very much time-saving).
- a diskimage of the whole sdcard.
If you want to stick to a certain LibreELEC version, store the installer program of that version in a safe place.