Fedora Platform 42 is in this case the runtime for Fedora Flatpaks. It should have been upgraded to F43, unless there’s still a Flatpak referring the old Platform (maybe because it hasn’t been updated yet). Try updating Flatpaks from the terminal, with flatpak update, then check if the old runtime is still there, with flatpak list --runtime.
EDIT: sorry @anotheruser , I just saw you advised the same thing already.