You can see my post about this 3 years ago after I played the demo and the devs reply:

"Glad you enjoyed! Hopefully later down the line we'll be able to add controller support; it's something that would definitely be useful. There aren't any immediate plans to add that though, sorry!"

I've given up hope at this point. They don't seem to care and have likely moved on to other things.

>:(
That's why we gotta drum up the hype again now that over 1mil people have Decks in their hands. I overhear people plenty often talking about these. They either have them or want them if they play PC games at all.

i came here for this! The devs can target a whole new audience of steam deck users! This game can run and not be a total drain on the battery. Its time to put more effort into making it steam deck compatible and introduce native controller support.