I ran into Error Code 84 while trying to link my Steam account. After some digging, it turns out this is a security lockout from Steam's side—usually because of too many login attempts or a glitch with the modern "ReactJS" login window. Quick fixes that worked for me and others:
Anyone else stuck on trying to launch Gamehub? I’ve been trying to get online for the last hour, but it keeps booting me back to the title screen.
GameHub logs detailed errors. On Linux (typical deployment):