https://plasma-bigscreen.org/

My steam controller will act as a keyboard and mouse. I wonder if theres just a cheaper, more available controller out there that does whatever it is the steam controller is doing. It seems to work regardless of the DE, shit even the OS as it does it on my Linux computer and my work windows computer. If there is something like that it might be the way to go.

I use ES-DE to access all my retro titles and such. You can use it with RetroArch and now you have an awesome emulation thing!

bazzite can be installed in steam mode so it's controller friendly console like experience

retroarch, faugus & kodi might be worth a peek

kde can be controlled with a gamepad (tho it’s a setting you need to activate first), but in my experience it was pretty janky. maybe it’s better now? it’s an option to consider, at least

they also have plasma bigscreen which works better with a controller, but since it’s pretty recent (iirc it only got added in plasma 6.7, the latest major release) i doubt it will be in debian’s repos

Directly, not familiar with any (unless you're willing to mess with SBC Android), but I would try using AntimicroX, a program to remap controller keys as keyboard keys and mouse commands, and then set it to auto-start.

An option to consider: LibreElec does this with Kodi, and Kodi itself can be used for this. LibreElec can be set up for a controller from boot.

The downside with Kodi is it's a bit clunky to do anything other than play media, but it can be used to launch games reasonably well or even launch a dedicated gaming interface like RetroArch for a good interface for games.

I'm sure you could achieve what LibreElec achieves using Armbian and DietPi if you're willing to spend some time configuring things.

Plasma BigScreen or Flex Launcher

I can't tell you how to do it under Wayland off the cuff, but you can map a controller's analog stick to act like a mouse. It's a little clumsy, but that'll let you use any mouse-oriented DE.

Some gamepads, like the PS5's controller and I assume the Steam Controller, have touchpads built into the controller that work as pointing devices.

If you don't specifically want only a gamepad, I'd probably use a trackball or touchpad and maybe keyboard, as a trackball can be used from a couch, lile a gamepad.

Do you have an existing controller you're planning to use, or will you be buying one? There are many small, inexpensive combination keyboards and track pads which work via Bluetooth or come with a 2.4 Ghz dongle. I picked one up for about $20 a couple of years back and it works great.

KDE Plasma. TheBlackDon on youtube does this with KDE/his KineticWe setup using a Steam controller.