I'm struggling with this problem as well.
I'm finding when I try and SSHFS with my TrueNAS box...
Assuming the user is cloudback
The path is /home/pool/dataset/cloudback
I set my backup path to /home/pool/dataset/cloudback and my prefix to full
Cloudron always changes the permissions on the directory /home/pool/dataset/cloudback to 777. This seems... grossly insecure. And, worse, it breaks SSH, because you can't have a filesystem above the .ssh directory with permissions that open.
However, I also find that if I set the path deeper into the account (with no prefix), I avoid the permissions issue, and instead, I get backups that hang/lock, especially on Immich. (That could be unrelated.)
My single biggest question is why is Cloudron setting perms to 777 anywhere?
I'm trying again by creating a directory in the homedir, and using that as my base path. Then, within that, I'm using the "path" option to create subfolders. I don't have a reason I think this might help, but given comments above, I'm trying it.