For me it isn’t working. Single player works fine. If Crossplay is ON I can see other games on the world map, but time out when joining the lobby. When I disable Crossplay I see none at all. (Yes, this is the opposite of what you might guess based on other issues people have mentioned where disabling Crossplay fixed it.)
If you haven’t, I can recommend checking the ProtonDB page. Sometimes you can find great tips on there. Might be worth a shot.