Sorry I cannot help you with most of your problems but I also got a lot of errors since my upgrade to Ubuntu 22.04 and the latest urbackup version. I don’t really know what is going on yet but it seems to me as if datto is not working properly. When I manually create images via datto they sometimes cannot be mounted which is why I for now disabled snapshots with datto completely. After disabling datto my Linux Backups run smoothly, before that I had lots of errors like „cannot get complete file“ and the like.
Regarding the datto cleanup:
I created a small script for cleanup. You may want to have a look at this and if necessary adapt it to your needs. You can find the script here: