An MVP is something that can be thrown away. Its purpose is not to evolve over time but to prove money can change hands, aka "viability."
An App is about distribution. iOS has the most money spent on its ecosystem, but outside of USA Google Play is more predominant. A web app itself is device agnostic. It would be the appropriate place to evolve to in order to avoid Apple's 30% commission. Apps do have their benefit, for example engaging the user with less distraction from a web browser. It also can load faster with offline data. Yet those are efficiencies for production once MVP is proved. Therefore imagine an MVP as catching salmon in a net, and app as a grocery store + Instacart system. Hope this helped answer your question. Let me know if not and I'd be happy to clarify over the phone.