Resolution: Information Provided
Affects Version/s: 2.4.0
Fix Version/s: None
This problem was noted with Gerrit using a 2.4.0 mina sshd server  after a recent upgrade. Some users using Fedora 33 started being not able to log in.
It turns out that Fedora >=33 has dropped rsa-ssh from it's default PubkeyAcceptedKeyTypes in /etc/crypto-policies/back-ends/openssh.config. You either have to modify your policy globally to "legacy" with "update-crypto-policies" or manually set PubkeyAcceptedKeyTypes=ssh-rsa for failing servers.
I understand that server-sig-algs support isn't fully implemented in mina sshd as yet, so the client will not be seeing the negotiation list.
However, it seems rsa-sha2-256/512 are supported? It seems like forcing this with ssh -oPubkeyAcceptedKeyTypes=rsa-sha2-512 should work, but it does not (see related gerrit bug)?
I can provide ssh connect logs, etc. if it will help; at this point I think it's mostly about understanding Fedora's change and any mina limitations so we can find the best solution for users. Although Fedora 33 users are obviously a small minority now, it probably flags something other distros will take up sooner or later.