Yes, but I don't want to force people to do that. I have after discussions with Claude (yes, the 'AI') and with Carlo V who has been incredibly helpful I've decided to put in a code hack. Both t30dpy and t30dpy3 check to see if wayland is being used and if so check the physical window size and if it is smaller than the startup size minus a protective margin they resize to that size. The protective margin is because an app can't query for anything useful or important like the task bar dimensions, so a fixed 128 pixels is used. Wayland and labwc also don't allow an app to specify where the window is to be opened(!), they decide. Why? It was considered a 'security issue' if allowed. Really? Insane.
Also noting again that p7sim suffers from the same issue. My modded version of that allows a size setting to be given on the command line so that can be used.
There is no reliable fix for an app window being able to slide over the taskbar, that is a labwc issue. That can be avoided by using a different desktop compositor like Gnome.
Just to be clear, this is also a problem only if your physical display is smaller than whatever size you start the app with.
Anyway, I'll check the changes in later today after more testing. Also note that vncs tend to perform poorly if there are rapidly updating images, like snowflake in t30 or in p7sim. This is specific to the pi5 running wayland and has to do with a lame implementation talking to the gpu.
All in all, Raspberry should at least be embarrassed. None of this is an issue on any pi other than the pi5, but you don't get the faster graphics gpu except on the 5.
Bill