Let's try forcing an update of the launcher.
Download the installer package for Windows:
https://forumcontent.paradoxplaza.com/emailsignatures/2020.12-win-prod.zip
Unpack the file you just downloaded and place the three files in the Steam folder for the game you're having issues with. If asked if you want to replace already existing files click "yes" - that's a sign you are in the right place!
Then please repeat the launcher reinstall procedure from before.
To the extent that your problem may be caused by our servers, that will not be fixed until then I'm afraid.
Have you checked your firewalls allow the launcher and game through?