Lutris lets you right click > Add to Steam

Its pretty quick

Boilr, was originally made for steam deck.

For ROMs, Steam ROM Manager should work for you if you're on a normal computer. If you're on Steam Deck you'll want EmuDeck.

For GOG games on Lutris, I can't really help there. Sorry.

Yes! You have decky loader with a plug in called Steam Grid DB which updates the art for these games really easy