i can argue both the switch and steam deck are massive successes. i dont know what it'd take to compete with the steam deck, but i saw many of the deck competitors managed to not have most of the input options as the deck. to ride off the deck's success, it needs to also fit into the deck ecosystem.

if it a portable gaming device it should have standard gamepad inputs, analog triggers, gyro, a trackpad, back buttons, and auxiliary inputs. it should basically have most of what the steam controller has and more. so any game can suit it comfortably.

I threw in all those extra terms like "massive" to try to hint at the difference between ~5m units sold and 143m units sold. That's a pretty vast difference and finding reasons why is the crux of the matter