I have 2 Xbox accounts, one for me and one for my son, this worked well on FH4, I could change profile in the XBOX game bar to switch.
My son has logged into his account and launched FH5, now it is stuck in his account and I can’t switch it to run my profile.
Any tips on how to run my own profile in FH5?
I change the profile in the xbox console companion app. You can sign out of a profile in the settings section,
Click “sign out”, then “not now”, when it asks you to try out the new xbox app (the new one is having issues, for me at least)
Click “sign in”, click “switch account”, type in, or choose the account you want to use and finally click on “let’s play”.
We have changed accounts several times this way yesterday and today.
Thanks, worked a treat 
My husband and I are having the same issue.
He started playing with his Microsoft account but now when I try and log into my account and open the game it defaults back to his. I am unable to start a new game. I tried the above but it didn’t work.
Any help would be appreciated.
My pc is enough to run this game(RTX 3070ti, 32gb ram, 5600x)
But it seems crashing at the title of the game and I found the error code “0xc0000005”
I tried everything that suggests online by Xbox and Forza support.
To my thoughts, cloud save files causes the problem.
So I really want to clean up my cloud, DELETE ALL THE SAVE FILES.
It’s been 2.5 years but if anyone gets 0xc0000005, try:
Reseating your RAM (worked temporarily for me)
Clean up your registry (permanent as long as you do it regularly, I’d recommend Wise Registry Cleaner)
If you still haven’t fixed the account issue or if anyone is in the same position then this might help
In windows. Go into settings and create a new “administrator” user account. I would advise local account despite windows trying to get you to use a MS login. I won’t get into the reasons why a local account is better and safer here because it’s not the problem at hand but local is always the better choice
This gives you another name on the login screen so he has his own windows profile on that machine
When logged in to this new account, sign into the xbox app and windows store app with a different ms/xbox account and it will be like playing on a separate system
From my experience, I have Forza installed on a separate non system disk (i.e. not the C:\ drive) and windows allows me to access the game from the second account without installation. I don’t know if the game installed on the system disk would change this behaviour or not but it’s worth a try
Game is stored at one location but your user data (save data) is stored in the users folder so creating a new user would separate data saved in a different profile so there is no risk of save clashes. windows has supported multiple users for decades and this is a very good use case for home use