Cannot start game normally without using SteamDeck=1 as reported by other users. After adding aforementioned parameter, game would start but show me black screen. After reading some other report, it appeared that game requires Steam account linked to PSN, which gets indicated by a new tab being opened in my browser (Firefox). I was not able to link my steam account to PSN, because when clicking on a button in browser I would get HTTP error "Parameter 'client_id' is malformed". After some more googling I stumbled upon this comment: https://old.reddit.com/r/Helldivers/comments/1cl3yyg/trying_to_get_my_psn_and_steam_linked_in_and/l3uv83b/ which involved a fair bit of URL manipulation. In essence you need to replace client_id=null and redirect_uri=null parameters in URL that causes error with values from original page (the one that got opened initially). After all these manipulations, after restarting the game, seems like it works fine. I use Arch btw.