When I bought the game I’ve installed a Forza Horizon 4 Ultimate Edition, which in it’s turn installed all necessary additions. And this was a mistake!
So if you installed your game by pressing Install button on Forza Horizon 4 Ultimate Edition and are not able to launch the game, try following:
Did this last night. Installed everything fine. Launch the game, crash, go to my library and somehow Car Pass and Ultimate Edition show “Install” when they installed already. Install again and it shows Error or simply does nothing.
You shouldn’t click Ultimate Edition at all, it’s a bundle and it fails to install correctly in some cases. That’s why one should install all contents manually. One of the other packages is also bundle of a 2 smaller once.