I am having problems with OSMC Backup and Restore utility as well. Posted about it here and got no response ( Backup done but how to restore ). Instead I was directed to the Backup addon, which works great. It can compress the backup and transfer it to a network location (in my case a NAS via NFS). It also gives you the ability to choose what to backup, including 2 entries that you can fully customize.
There is also the other option of creating an image of the SD Card itself. It takes a lot of space (basically the size of the SD Card) but if you have a linux computer and know your way around it, I think it is possible to only image the boot section(?). I’m not experienced in linux so I haven’t tried that approach.