Interesting info in that link however it does not apply to my situation. I am on PC and the info in that link applies only to consoles.
The only reason that I have 2 MS accounts/Xbox acounts is that the original account’s (A) email became definct/compromised during a period when Microsoft would not allow you to change your email on an MS account. I had to make a new account (B). So in my case there is no real ‘sharing’, just me.
All games are bought on the B account and are only used on the original Xbox account A. I am happy if they ‘move’ all xbox game purchases made on the B account to the Xbox A account so that they cannot be accessed by the B account. I do not want to share, I just want to use the Xbox account that has all my achievements (such as they are) etc on it.
In addition I installed the game from the Xbox app whilst logged in on the A account. Every Forza game before this has had no problems doing it this way. Why would I even think in the furthest reaches of my mind that I would not be able to access what I am installing? Nothing anywhere stated anything in this regard that would lead me to believe that I could not use the premium content as advertised.
I have been told by a person via the Xbox support link that their friend had the same problem as myself and Forza support put it right for them…we will see if this was just to get me off the line or if it was actually true.