I'll try to explain this as good as I can:
I upgraded from a GTX 970 to an all AMD build with a 5700 XT. I use displayport to my 144hz monitor and have a 2nd 'screen' with HDMI to my receiver for the sound (so this screen is invisible, 800x600 tucked away at the bottom left of the main screen, so purely for the sound).
With my 970 in Forza 7 I could just run the default settings and got 72 fps (so v-sync half of the 144hz). With my 5700XT, it defaults to 60fps, and only when I disable or unplug the 2nd 'screen', it defaults to 72 fps (and this is with a 'dynamic option, the other options: 60 fps, 60 fps v-sync, unlocked and unlocked v-sync, dont work well too, so I would like to just use the 72fps option).
Also, freesync doesn't work at all, but this might be the game or the fact that it's a UWP game.
So bottom line is:
Before with my 970 the game detected my 144hz screen and gave me 72 fps, now it 'thinks' my screen is 60 fps (and this is my 2nd screen), so there is no option to have it on 72 fps. Is this a driver issue?