This method should fix the installation of the Paradox Launcher failing to install when trying to launch the game through steam.
Delete These Files
Locate the game directory.
Delete the files called, launcher-installer-windows.msi & launcher-settings.json.
Once you have done that, right click the game, properties.
Go to local files and the verify integrity of game files.
Once all that is done, just hit play and the launcher should start the installation process.