Can you send us your player logs?
1. Boot up the game, try to log into the account, then try to log into guest mode. (This should fail.) Don't quit the game, just leave it as is!
2. Send your Player Log. To find the right file, put "%appdata%\..\LocalLow\Innersloth\Among Us" (no quotes) in an explorer browser and find the file Player.log or Player
3. Email that file to support(at)innersloth.com, subject line: "SteamworksAuthFail"
We'll get to figuring it out!