I think the threat of Meta forcing users to migrate to a hypothetical 3rd party app store is overblown-

https://news.ycombinator.com/item?id=30808926

Now, they might try to entice users with deals and such (sort of like Epic's gung ho free games discounts on their gaming platform against Steam), but I highly doubt they'd pull their apps from the official App Store. Too much risk of blowback.