Valve announced a change for Steam today that will make things a lot clearer for everyone, as developers will now need to clearly list the kernel-level anti-cheat used on Steam store pages.
They do give a refund for this. I got it after they added it to EA Sports WRC. Explained to them that it was not in the original contract and that it prevents me using the product I licensed on Steam Deck and GNU/Linux and they refunded me.