Not sure. Might be because of other mods, your screen size or your gui settings.

Had the same problem. Tried full screen, windowed mode and different resolution settings. Had no other mods installed. Nothing working.

This was the solution in my case:
Common issue. Try these ideas taken from another thread:

The usual fix for mod issues under the new launcher is to:

Go the HOI4 mod folder (under Documents) and delete the *.mod files. In fact unless you are creating mods yourself the directory should be empty.

Start the new launcher. Turn all mods off. Start a new vanilla game and reach the main menu. Exit.

That should result in *.mod files being recreated in the HOI4 mod folder with current timestamps.

Launching a new game from the launcher will normally work.

Source reddit: https://www.reddit.com/r/hoi4/comments/e5jqpq/new_launcher_not_loading_mods/