Appreciate the help regardless. With anything new there’s always the question of “is it a newbie thing and I’m doing it wrong or …”?

Thanks for the suggestion. Unfortunately I keep getting an error “Could not find any non-steam apps”. I suspect this is because this is a streamed game and not locally installed.

I’ve now determined that it’s not just non steam games, it appears the Decky <-> SteamGridDB plugin is not working as it should. I’ve restarted / reinstalled both a number of times now, but it just spins while trying to load up any images. The manage screen does actually work, so I may just hang on to the plugin for that reason alone, since manually doing it through each screen in Steam is painful.