Steel Century Groove and Steel Century Groove: Midnight have always played great on the Steam Deck, but I wanted to make a post to officially announce that!
In fact, the Steam Deck has been my primary device for developer playtesting for over a year. Performance is good and all the game's features are supported, including custom music!
And if you don't take my word for it, here's a quote from RPG Site's preview of the full game earlier this year:
"Visually, the game looks quite nice - and absent of the official Valve seal, we can say it runs perfectly on Steam Deck, as that was the setup the preview was based around."