I'd like to post the following news item within the hour.
Title: sshd needs restarting after upgrading to openssh-8.2p1
Conent: After upgrading to openssh-8.2p1, the existing SSH daemon will
be unable to accept new connections. When upgrading remote
hosts, please make sure to restart the SSH daemon using
`systemctl restart sshd` right after `pacman -Syu`.
I deeply regret not spotting this while the package was in [testing].
And I also regret not being able to diagnose what the exact problem is
just now. Given time is of the essence, I propose posting the above news
quickly even I don't consider it a very satisfying solution...