@wookapotomas Thanks for the info!
Thing is that I never had to use GLOSC before as everything just worked with either my Switch Pro Controller or my PS4 Controller, and I would prefer to keep it that way.
The method described on reddit also gives issues that it appears to be without the Steam Link, as they start with mouse and keyboard and then turn on their controller, but for that to work for me I'd need to start up the steamlink, go to big picture mode and then connect to the game, which is not possible. The Steam Link will just stream the images, but will not let the controller take over the controls of the game in my case...
Finally got it working again last night - haven't been able to play since the title update. Streaming via Steam Link on Apple TV using a DS4 controller.
Launched the game on Steam Link via the steam shortcut (just the normal Valhalla exe. Not added using any of the 3rd party programs).
Connected the DS4 as the game was loading and got the controller connected popup during the startup videos.
Controller wasn't working on the main menu (as in game thought I was using KB/M) - same issue as above - Steam Link just streams the images but doesn't seem to recognize the controller.
Went back to PC, into options and changed the controller from KB/M to Xbox Controller. Worked fine from there - good to be able to play again!
So definitely an issue when starting the game through Big Picture with a controller. Seems fine starting with KB/M and then switching once in game. Hope it gets fixed properly soon but in the meantime hope this workaround helps!