I expect Halo Infinite and Forza 8 to be launch titles for the next xbox. Possibly crossgen. Holiday 2020. Gears 5 on Xbox One won't screw them.
I think there is a near 100% chance that the next Halo is a launch title for next gen. As for Forza, I'd figure they want to launch with a Horizon game, if possible, as it is a bigger seller.