There was an update from Zoom in early August 2023 (I forget the exact date) that has broken screen share completely for me and partly for a colleague who also uses Linux.
We both have Ubuntu 22.04 LTS machines, reimaged onto Dell machines that were originally windows.
I won't write more details because after a search, I thought it might be due to Wayland, and it was. So I will add my answer here to help others find it.