[2021] [Arch Linux] Multiplayer desync/ lag unless hosting, even then game lags behind

Has this always happened ever since you've had this game? Or only since when?

Does this also affect our similar games Stellaris, CK2, and HOI4? Or only EU4? because they use the same MP services as EU4.  

The last major update of EU4? I guess that would be 1.30 released on 9 Jun 2020 - you've had this problem ever since then, over 6 months?

You should check that all the required Steam ports are allowed through all your firewalls, as the new eu4.exe. in that patch may not be in your firewall exceptions lists:

Steam Support :: Required Ports for Steam

support.steampowered.com  

Can your friend play this game with some third person without this issue?

Any chance you can try it via a VPN? Or from a different machine or even from a different network?  

Roberto258 said: A port issue it is not, as the Arch Linux default configuration have all ports opened by default.

Ports can also be blocked in the firewall in your internet router/modem or even at the ISP.

However that can be worked around by using VPNs, or now you can opt into the new Nakama MP service instead of using Steam MP - if all players choose that at game start is it any better?