I use a magic arm originally meant for photography work, e.g. holding a reflector or camera highlight flash. Brand mostly doesn’t matter, but at the weight of a Steam Deck, you don’t want garbage. Specifically, I use a Newer because I’ve had great luck with their stuff has been consistently good over the years. To hold the Deck, I have a Ram Mounts tablet X-Mount, which keeps the vents and buttons juuust accessible. I usually use a Bluetooth game controller. Works great anywhere I can clamp the base.