This is a strange way to phrase the question. Sites that had to shift to app-like experiences are hard to find, because nowadays pretty much every web app is an app-like experience from the beginning and is created with a JS framework. The shift happened years ago.

Barring informational sites like blogs and news publications, it’s actually more challenging to come up with new web products that are NOT app-like in nature, and that do not use any kind of JS framework. Craigslist may be one of the few big ones and even it is losing market share to FB marketplace, which is an app-like experience.