I'm having the same problem with my son-in-law...
Go to your games library, right click the game and select properties, select controller, then change it from 'use default settings' to 'enable steam input'. Also just use the x-input option on the back. You'll have to do that for each game you use that controller on. this enables 'generic controller' support.
Already tried that. Maybe I should switch to SteamOS
Yeah maybe, what has you on Pop OS or whatev? Never even heard of it
It's based on Ubuntu and was supposed to have support for a lot of devices out of the box.
xbox controller works flawlessly with steam under linux. As long as I connect it before i launch the game. A few games pick it up after, but most do not.
Arch based distro here. (steam deck is arch also)
I have no experience with the controller you bought though.
First step would be to open a linux designed controller game, outside of steam and get it working on that. Think minecraft outside of steam.
Make sure the controller registers and works there before steam. if so, the the problem is likely on the steam input side of the problem. IF you cant get the controller working outside of steam in a game either, its likely going to be a driver issue for the device not working.
What I am finding in quick searches about that controller is that people got it working by getting the xbox controllers working.