New Xbox - can't share games

Hi, hopefully someone can help me out here with a solution to a specific problem I've been having.

It's important that a few things are completely understood about my situation first.

First of all, I just upgraded from an Xbox One to a Series S.

Secondly, my son has a Series S as well.

Thirdly, and very importantly, we had been sharing games and an Ultimate account with no problems previously. I could see a few of the games he bought on his console (important to note they were purchased on his console) on my console in "My games and apps" but could not play them because they can't play on the One. He bought FIFA 23 on his console and I've been playing it since release day on my console - I never bought it. And, crucially, I never had to sign in as him on my console to play the game. His profile was on the console, as it is the new one, but I never, ever had to sign in as him to play. He is usually upstairs playing his own console, usually playing the same game.

So when I got my new console I set mine to "Make this my home console" without much thought. Somehow everything that was working on the One is not working on this new console. I can now only play FIFA 23 when he is signed in on my console. If he isn't signed in I get a message saying "The person who bought this needs to sign in."

I have turned off "Make this my home console" and turned it on on his. He has access to my Ultimate Game Pass.

So taking all of this into account, what should I do to return to what I had previously? I am running out of switches for My Home Xbox and don't want to lock it out. I only have two left. It would be really useful if someone could tell me what I need to do to make this like it was before.

Please bear in mind that I have had this working fine with no problems previously, and it's really frustrating that it isn't working now.

It would be helpful of someone could tell me who on each console should be ticking the "Make this my home Xbox" to get this working correctly. I've been gaming for 40 years and finally hit my first brick wall here, so I would really very much appreciate an accurate description of what to do. Thank you so much in advance.

:)