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.)
Update: I switched to Proton 9 from the Cachy version and it works!
Haven’t touched helldivers in a bit, but I did play it on cachyos back when it was released and never faced any issues. I don’t know if any new updates on either the cachyos side or helldivers side broke anything, sorry.