Backups - are they made less effective when either Roon or Windows is updated?

I also wonder if minor changes, like deleting albums, causes any confusion if an older backup is used.

As a Roon customer for 8 years I’ve only ever had to use the backup once but Roon and Windows have both been updated many times lately so the relevance of a slightly earlier backup concerns me. Anyone know?

No because a backup completely replaces/overwrites the current database.

If not done so already, set up automatic database backups, as described in the knowledge base here, and you should be able to recover to the newest working state after something bad happened.