Use a specialized gaming VPN or a tool like ZeroTier/Hamachi to create a virtual LAN between the two computers. This bypasses the ISP's restrictive NAT entirely. What router model you are using
May your jumps be true, and your errors random. 6023 parsec error exclusive
Beyond the Static: The 6023 Parsec Error and the Ghost of Lost Connections Use a specialized gaming VPN or a tool
If error persists after the above: