After Update to 20.0.9 Nextcloud reports version 21.0.1

I recently initiated the Update to version 20.0.9.
After the Update Nextcloud reports 21.0.1 as the version number.
I don’t have MySQL 8 yet on my server and am now expecting trouble.

NC21 runs perfectly with PHP7.4 (and php 7.3) as well.

Yes, but also MySQL 5.x ?
I’m expecting trouble there.

sorry read it wrong… of course this could cause troubles since it was not recommended for several versions ago, already

System requirements — Nextcloud latest Administration Manual latest documentation

That is the real issue here. There is a bug report for this:

and specifically for your case: