JoyKeyMapper 4+

This is the only app I could find that will let me use a controller with 2D Steam games on my M1 Mac on Big Sur. Until Steam updates controller support, this is the best we get. It worked fine on 2D games that don't require a mouse for looking around. You can map the mouse to the right joystick and it does control the mouse pointer on the desktop, but for some reason it doesn't translate to looking around once you are in the game. So you can move around in 3D games but not look (which makes 3D games unplayable).

Otherwise, I applaud the developer for his effort and making the app free. At least we have something to play 2D Steam games until Valve gets it together. I wish it supported PS4 controllers, but luckily I have a Switch controller so it works for me. If you can manage to get all planets in alignment and you're willing to put in a little effort, you can have a good experience playing 2D games on your M1 Mac thanks to this app. The M1 chip is a beast and I can play games I could never play on Integrated Intel Graphics. It's just a shame these companies won't work together to give us something as basic as native controller support in Steam. Hopefully it is coming...

It works well for the most part. However, I wish it had the option to customize options for multiple taps or long presses of a button on my controller. I had this feature on Windows. Also, it prevents my MacBook from sleeping. So if I don't quit the app, my screensaver doesn't activate and my screen doesn't turn off. That's annoying

It just totatly ignores my Xbox One controller. I know it's connected. I see it in my bluetooth and I have a tester app that sees the input from it.
This app just doesn't see it. Also, I see another problem that, even if it did see my controler, there's no way to bind 2 keys to one button. For example, you want to have a button do "Command W".. well, forget about it because this app only seems to do one key at a time, which I might have been able to test, if it actually detected my controller.
Having said all that, meh. It's free, so I'm not super angry. If I had paid for it, I'd be requesting a refund.