[2021] Connection Error with Host

Originally posted by 8bitOriginal: Having this same exact issue right now. Even had the friend over so we had three accounts running off Google Fibers top notch speed/bandwidth. Two of us had no issues, either hosting or joining. Third guy can connect to lobby, but it refuses to start a game he is in lobby for, and he gets immediately kicked if he hosts. Game is whitelisted in NORTON, and all necessary network permissions set properly. No clue why this is happening. Every other multiplayer game tested on Steam works just fine (barring problematic servers like Borderlands 3).
He is on a ASUS ROG STRX G732LXS laptop...
i9-10980HK
16gb DDR4
RTX 2080 Super
500gb NVMe for OS
2tb NVMe storage
Windows 10 Pro

Do the problem occur when he is joining any lobby/hosting any lobby with random people or just joining lobby hosted by both of you who is fine with matchmaking/hosting lobby and playing with both of you?