If you are trying to launch Mount & Blade II: Bannerlord - Beta, you can't because we have ended the beta.
If you are trying to launch the main game, can you please check the mods tab in the launcher and take a look at the module versions?
The module version located on the bottom left is outdated and it is a known issue. If you see e1.0.6 on the modules tab or in the news image of the launcher the game should be up to date.