Maybe. However, I have several devices running 21.02.3, most notably the AP (MT7621AT) and my main router (X86-64), none of which exhibit the problem. I also think if it were a problem with 21.02, we would have heard more reports by now.
I will set up some other device on a different target with a 22.03-rc and put it on the network to see if the problem is reproducible. Let's see what I have lying around
Edit: an R6220, that will do.
Edit 2: 30 minutes in and SSH is still up and responsive. So that's a "fail", the (or at least: my) problem doesn't seem to be universal to the 22.03-rcs. Next up I will test again with the MBL that gave me the issue first and try to reproduce it.
Edit 3: "success" I guess? 22.03.0-rc6 on the MBL, as before, fresh install from official download, disabled firewall (no dnsmasq or odhcpd present), no other software installed. SSH through wired clients on the network works fine. SSH through wifi (again, external AP!) prompts an established connection syslog entry after a loooong wait, never makes it to the login prompt before timing out.
Edit 4: The fact that LuCI works fine even when SSH fails makes me think it is some kind of dropbear issue.
Edit 5: Well, that is getting weirder and weirder. After some 10 minutes, somehow it ... "recovered"? SSH is now again possible as if there was never any issue. After googling the issue with dropbear, some (older) posts suggest it is a 5GHz issue, so I tried 2.4GHz in between, with no different outcome, SSH was still timing out. But then all of a sudden ... it recovered.
Edit 6: ... aaaand it stopped responding to SSH again, some 5 to 10 minutes later.