Debian 10 (Buster) keeps on complaining that ClamAV version 0.103.6 is outdated and I need to upgrade it to the latest one, ClamAV 0.103.7. However, it won't let me install from packages and says that it is up to date. There are some new packages missing. I can of course force install these missing packages but the question is won't it break anything? Plus, what's with the outdated message when it is up to date in Debian 10 (Buster)? ClamAV 7 is only for the latest version of Debian, which is 11. Debian 10 (Buster) has to run on ClamAV 6 only as far as I understand, but... it complains and "wants" ClamAV 7.. I am a bit lost.

Would appreciate any comments, suggestions, ideas at all. Many thanks in advance!

So basically the version of CLAM is out of date in your version.
If you upgrade to Bullseye (the actual current version Debian 11) it will still be "out of date" in those repos as far as I know. I'm on Debian Bookworm (currently testing aka Debian 12) and it is just recently current with the CLAM version.
You should still have the latest malware updates that are available (to my knowledge) in the Debian version your on.
The other option (if you like to play in Dependency hell) is download the source from the Clam site and compile it yourself, or see if it's in Backports (which I kind of doubt) for your version.

I hope that makes sense.