@rugby - thanks for pointing this out…
Although I mentioned in my Tech Support Request that File Explorer could not access either the internal SSD or the attached USB drive, I now see that Roon cannot access the USB drive either…
I’ve already got a (reported) issue that Backups fail, now I have another because the USB drive holds my Backups.
It should look something like this (this is an old screenshot from 2022 - the drive is still the same one):
