Algorithms: who's at fault here?

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

I recently tried to ssh to a recently-installed Linux machine at work.
Algorithm negotiation failed.  On turning on verbosity, this turned out
to be because, to edit the log down to relevant lines:

remote banner string: SSH-2.0-OpenSSH_8.9p1 Ubuntu-3
...
ssh: my algorithms:
...
	hk: ssh-rsa ssh-dss
...
ssh: peer's algorithms (%=unrecognized, *=disabled):
...
	hk: %rsa-sha2-512 %rsa-sha2-256 %ecdsa-sha2-nistp256 %ssh-ed25519

Looking at 4253, the only algorithm for this list I see as REQUIRED is
ssh-dss (though ssh-rsa is RECOMMENDED).  I've gone through the updates
I can find to 4253 (6668, 8268, 8308, 8332, 8709, 8758, 9142) and I
don't find anything removing ssh-dss from REQUIRED status.

Am I missing something?  It sure looks to me like either OpenSSH or
Ubuntu (whichever one decided to do this) gratuitously breaking interop
by desupporting a REQUIRED algorithm.

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