I just did a clean reinstall of Windows 10 because it felt its structure was being held together with ropes and ducttape.
After a fresh reiteration of Windows it feels butter smooth again.
Reinstalling Forza Horizon 4 again was a pain in the smoink as apparently the Store can't detect older files. In fact, the Store app just decided to wipe the folder the data it was in and started to download those same files again!
After that pain was done I wanted to get back in again but then this error came around saying I am not able to sign into Xbox Live currently and should try again later. Around 24 hours later it still says the same thing.
Also you can press the error code as the window clearly states: "If it still doesn't work, we have a few suggestions which might fix your problem.". But when I press the error code I get to a page which tells me the error code doesn't even exists! Well done, Microsoft...
I can't contact Microsoft because it's the weekends right now and having searched on the web a bit a few other people had this problem (not just in FH4) and Microsoft couldn't fix it. Or at least they didn't finish the topic to show the answer at least.
I can log in here and on the Xbox application on Windows itself, just not on the game. So, what now?