Forza Horizon 4 won't launch

It's disappointing because I do enjoy the game when it runs. Hopefully the devs will get some visibility on the issue and the resources they need to fix it.

I Have been having the same problem. I bought the standard game,my grandson built up 2million cr in a week,so stupid me decided to get the ultimate add ons….dam it!  Yes you guessed, it stopped working. I was online to a Microsoft expert for whole weekend trying various options,but it is still not starting. get the flash start picture for a minute then nothing. Uninstalled many times wasted hours thru the night downloading ,over and over.usually I find a solution, but im stumped. set it on different drives .now have requested refund on the add on. we will see what happens,but was told you cant un install add ons.?? Cost money these games and they don't make it easy to get refunds or help.

Of course this has happened to me aswell, so I tried every single possible solution I could find online but nothing has worked, obviously.

BUT, I have contacted first Forza Support, waited 20 hours for a reply only for them to tell me it's something wrong with Microsoft Store. Then it took me an hour to find this discussion and find the link to actually chat with an Microsoft agent instead of having to phone call them, which is great. I talked to the Microsoft agent about the situation and he said he has checked everything on my side and his side and everything seems to work fine. After our chat ended he sent me an email which I was supposed to forward to Forza Support which I obviously did. They asked about PC specs and that **** which doesn't matter and finally said that they are investigating this issue and working on a fix finally. Now we wait I guess

Have you had success with that? I tried as you recommended and the tech just directed me to Playground support to see if they had a solution.

They haven't fixed it yet, since I only contacted them about it Yesterday, they told me it will take 2-5 Workdays for their team to review my account.

Here is the link: https://partner.support.services.microsoft.com/en-us/contact/chat/21/

Good luck fam!

Have you tried contacting Microsoft Partner support? Not Forza support, as they imply they can't do anything about it, since it's a license issue on Microsofts side. I can give you a direct link to a agent if you want to. 

The person I spoke to said it was a common issue with people having Xbox Game pass or people with two copies of the same game. 

I'd like a link if you wouldn't mind... did they fix it??