[2022] I can't log in inside EU4 game (so I can't join multiplayer games)

If you use Windows Defender firewall, both eu4.exe and paradox launmcher.exe need to be allowed in both the Private and Public columns there. If you use any other firewall it will have a similar function.

If that doesn't help, can you test by connecting to the internet via a VPN or a mobile phone hotspot? That will rule out any firewall between you and us.  

If that doesn't help, can you test by connecting to the internet via a VPN or a mobile phone hotspot? That will rule out any firewall between you and us.  

That shows this is indeed a firewall issue somewhere - either within Windows, your internet router/modem, or your ISP.

If you use the Windows Defender firewall, eu4.exe needs to be in its Public and Private exception lists.

Otehrwise it's probably time to contact your ISP, especially if they supplied your modem.