No, it didn't. I was using Wayland as well.
Are you sure that Wayland doesn't effect desktop files?
In March of 2020 in regard to desktop icons in Gnome, version 3.28, the developers decided that it would be better to disable this functionality altogether.
Could it be that the functionality is still disabled and that's what the problem was?
Searching here this afternoon to try to find out why I couldn't produce the same results that you did with FF.
FWIW, a friend of mine running Zorin LTS installed Alacarte and created a desktop file as well.
He explained that, . In Debian I was not able to follow the path to the executable using browse until I had added the icon in properties.