I’m running a Steam OS like experience on my Lenovo Legion Go. Not quite a steam deck, but very similar.
You should be able to use the heroic launcher. And you should be able to install it as a flat pack or a snap. That will make your GOG games as easy to download and install as a steam game. If I recall correctly, it even automatically adds entries for steam.
I regularly play Bomb Rush Cyberfunk on this device using the GOG edition.
I’m really surprised no one mentioned Terra Invicta!
Basically if the Three Body Problem series was a Grand strategy game.
In terms of grand strategy it is quite grand. So massive and complex that even 100 hours in, I haven’t completed a game.
That being said, it’s so addicting. I haven’t really played any other Sci-Fi games where you can take over multiple countries on Earth, take over other bodies in the solar system, and field space Navy to defend the planet.