Remove the
+NetDriverDefinitions=(DefName="GameNetDriver",DriverClassName="OnlineSubsystemSteam.SteamNetDriver",DriverClassNameFallback="OnlineSubsystemUtils.IpNetDriver")
line from your DefaultEngine.ini, that you added. That line instructs your client to use the Steam P2P Network Driver instead of the more basic IP Net Driver. You do not get automatic NAT punching with the IP Net Driver.