I have noticed a massive loss of performance in the openssh-client package. It has no impact on a raspberry pi 4 because it has enough CPU power, but on a pi zeroW it took about 10 seconds until the command prompt is shown to enter the password (or autologin) while CPU load is 100%.
It can be reproduced very simple:
On a Pi ZeroW open a terminal and connect to a ssh server.
It has worked before, but then "Raspian-2" version was replaced with "-2+deb12u1" which has this problem.
Working: OpenSSH_9.2p1 Raspbian-2, OpenSSL 3.0.11 19 Sep 2023
Problem: OpenSSH_9.2p1 -2+deb12u1, OpenSSL 3.0.11 19 Sep 2023
As you can see, the version number is the same. But the description is different.
It looks like something like hardware acceleration is missing. If i replace /usr/bin/ssh with the "old" one it works perfect. Login prompt is shown in about 2 seconds. But with the new version it took about 10 seconds until the prompt is shown.
Please let me know if you need any further information.
Working: OpenSSH_9.2p1 Raspbian-2, OpenSSL 3.0.11 19 Sep 2023
Problem: OpenSSH_9.2p1 -2+deb12u1, OpenSSL 3.0.11 19 Sep 2023
Neither of these are Ubuntu packages.