Your scheduled backup is configured to backup to D:\Backup. So why did you post a screenshot from the properties of D:\Roon? Is that where you pointed the Backup manager to look for backups (hint: they aren’t there)?
I wish it was that simple. I posted this screenshot to show the size of a single manual backup, which I put there. The automatic backup pointed to d:, “Backup” being the volume label, not the directory and not to be confused with subdirectory “Backups” that contains backups not related to roon.
I attached more screenshots to illustrate this. There is a subdirectory at root level holding the files resulting from automated backups, see screenshot. Size is close to 200 GB.
Selecting drive D. as source for restore or housekeeping returns zero results.
Maybe that is the issue here. I don’t know the internals of Roon’s program code in place here, but thinking about the fact that the same code based on the .NET framework is used for all supported platforms, using the special case (drive letter) that doesn’t exists in that way on other platforms was probably not wise. Even in Windows the drive letters represent a special case including special rights.
I would try and create a new scheduled backup task, using an actual folder as backup target and see if that works.