I did an in-place upgrade of my Windows Server 2016 to Server 2022, here are some issues I encountered.
Installation
I had major problems with the services at my data-center, that had nothing to do with Microsoft.
When installing the OS 1% progress took about 20min, the ISO was mounted into the VM in a very weird way.
In the end I copied all files from the ISO to a location on the VM and started setup.exe from there.
The whole process took about 50min for me. About 35min for the installation during which all the web sites were still running.
At some point the screen tells you it is about to reboot but doesn't wait for a confirmation.
In my case a ping didn't respond for about 3min, the web sites were down for about 7 minutes, and back up while the installation was still in progress.
Console logon and RDP worked again after about 16min. This will all depends on your hardware. This was all on a VM, bare metal would take much longer.
Desktop???
The first thing I noticed after logging on was a desktop with a Microsoft Edge icon on it. Previously I got just a PowerShell window which is enough for me on the server.
Yes, I still did install the Desktop Experience, not server core, but I had changed the shell to be PowerShell.exe rather than Explorer.exe before, so the upgrade removed that setting.
So much for "keeping your settings".
TLS 1.3
Client Certificates
I have a few web sites for which I use client certificates for authentication, none of those worked any more:
Hmmm can't reach this page
The connection was reset.
I am not sure what exactly does not work here, but I solved this by opening IIS Manager and selecting the https Site Bindings dialog.
Here I checked: Disable TLS 1.3 over TCP and the connection with client certificates works again, but of course only in TLS 1.2
I have to investigate this further.