I don't think the number is around $50B but more likely $15B but you're still right; this is far more than enough to run the App Store. YT makes similar revenue

I don't think the number is around $50B but more likely $15B but you're still right; this is far more than enough to run the App Store. YT makes similar revenue to the App Store but likely spends considerably more OpEx given the nature of the service. But no one really expect YT to be net-loss for Google. This is especially true as Apple consistently claims that the App Store is an integral, inseparable part from iPhone; so even if Apple loses a significant amount of money from the App Store it should be fine as long as iPhone can make ~$100B profit each year. Of course, they could invalidate this logic by introducing some form of competing app stores, which would be just nominal in practice, but they didn't choose to do that. I don't know why; no one really can compete with Apple in the iOS ecosystem and this would significantly mitigate their legal risk.