I’ve had to restore my Roon ROCK twice last year year due to sudden power outage. This caused my Roon database to be corrupt and below is some links to the issues I had.
I do the same a you, keep 4-5 backups and backup of Roon database every night to my Dropbox.
This might not be the best solutions as you mention, if backup day 1 has something corrupt and then it’s overwritten day 6, but restoring from my backups have been successful every time for me.
Best way to do a 1:1 backup, would be to clone the NVMe SSD inside the Nucleus to another NVMe with same size. I had 100% success using this when I upgraded from 512GB to 1TB NVMe SSD for my PC earlier this year. I’ve linked the cloning station I used below. Using this cloning station does not need any PC software and cloning is done from the button located on the cabinet.
The NVMe in the Nuclues only contains your database, playlists and etc. Music is as you said is stored on the SSD or NAS. Only downside by cloning the NVMe, is that you need to take a part the Nucleus every time and maybe not the solution you want. But, for a “full” healthy backup, it’s might worth to do it sometimes during a year 