Using a game engine for UI and making the style of the interactions the game-like are two different things.

Game engines are generally capable of creating hardware accelerated 2D UIs which could be great in some cases where highly dynamic UIs are desirable. But making a business app 3D for no reason is a different story.

The later is largely what "The Metaverse" as Zuckerberg sees it is trying to accomplish. Check out Horizon Workrooms and the like.

I've worked at a number of agencies over the years and at one point years back a client insisted on Unity for their mobile app because it worked cross platform out of the box. It was an unmitigated disaster because we were trying to fit a square peg in a round hole. Tens of thousands of dollars wasted.