I had this problem with friends when trying to play with them, recently found a fix that’s fairly easy to do!
Remote Play with Your Friends!
Literally start remote play, the friend with their controller plugged in wont see their controller on the screen to begin with.
Go to shift + tab steam overlay, make sure your friends are connected.
Press on the controller button at the bottom and then you should be able to change their controls from WSAD (Keyboard) to the controller layout they need, generic or whatnot from steam itself.
After choosing either the rayman layout or just a generic controller for your friends (Either one should work). Your friends should be able to join by pressing the hit button.
Was looking on how to do this for ages and couldn’t find any help online, figured this out just today.