Press it long enough for the Steam button shortcut guide* to pop up and it goes into mouse mode, click it twice to open and close the sidebar to go back. That’s how it’s supposed to work at least.

^(*You can also use the triple dot button to do the shortcuts. So triple dot + X opens the keyboard etc.)

While you can’t really use Epic or Origin, sure, there are quite a few stores that sell legit steam keys. IsThereAnyDeal is a great source for checking and tracking them E.g, Horizon Zero Dawn, most if not basically all of those shops will give you a key you activate on steam.

Hm, I would have assumed booting from the micro SD would work. Does it not?

Valkyria Chronicles, Slay the Spire and One Step From Eden are the one I have on my deck currently.

And a bunch of visual novels. So, so many visual novels.