Hi there! My name is David. It’s a pleasure to help you today.
Thank you for posting your question.
Do you get any error when trying to download the game?
Did you have the game installed before?
Keep in mind that Forza Horizon 4 is no longer available for sale in digital stores since December 15, 2024. However, if you purchased the game before that date, it should still be available in your library and can be downloaded and played normally.
If you purchased the game from the Microsoft Store, I can suggest the following steps to find and install it:
Sign in to the Microsoft Store with the same Microsoft account you used to buy the game > at the bottom left, look for “Library” > click on “Games”, then look for "Forza Horizon 4" and try to download it.
You can also search for it in the Xbox App > Sign in to the Xbox App with the same Microsoft account you used to buy the game > go to “My Library” → “My Games” > select “Owned”, then look for "Forza Horizon" 4 and try to download it.
Let me know if the shared information has been helpful. Regards.