This is what I’ve done for years. It just auto starts after OS launch in big picture and I grab my controller. Occasionally I have my wireless keyboard for something but it works fine.
I don’t own a steam deck they’re not available from valve here in Australia. So I’m sure I’m missing out on some polish. But I’ve never seen it so I don’t miss it.
People come over, sit on the couch, grab a controller, steam is loaded, they play game. The OS and then steam is out of the way in a flash. After all I’m after the game not the launcher.