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