I’m at the limits of my using the proper nomenclature so please bear with me.
I often ‘ssh’ into my server and start an app which displays on my laptop. I believe that Xorg handles this in Ubuntu 20.04 LTS.
It’s my understanding that 22.04 will use Wayland to handle this situation. If I upgrade the laptop (the client machine) from 20.04 to 22.04 but don’t upgrade the server will the two computers be able to communicate? Or are Xorg and Wayland incompatible?
I don’t have an answer to your question about if a server on xorg can communicate with a machine on wayland. But in 22.04 it will be possible to switch between them.
here a page that tells you how.
how to turn off wayland in 22.04
I guess, in your scenario this shouldn’t be an issue, at all.
However, I would recommend setting up a virtual machine with that Ubuntu version that has Wayland as the default and then reproducing the scenario. This way you can be sure that it will work, if the upgrade goes well, in the first place.
In any situation, you should create a backup before doing any upgrade. This will also help you from getting out of other issues in your remote desktop scenario, if things go not so well.