After having had Gears of War 4 multiplayer be 60 FPS (both XBO-S and XBO-X), there would be a riot from the player base if they even attempted to lower it to something less than 60 FPS in multiplayer (which is the footage we are looking at and you are commenting on).
As for single player, I'm sure the XBO-S version will be 30 FPS while the XBO-X will have both a 30 and 60 FPS option just like Gears of War 4.
It'd be interesting to see how many (or how few) XBO-X owners chose 30 FPS over 60 FPS for the single player. I'm sure MS has the data, but no way for us to get access to it.
Regards,
SB