Are web pages served within apps reported as a “web” or “app” platform?
It depends if the page is opened as a native page in the app or a embedded browser page.
If a page is rendered natively in the app (e.g. the app will download the html file and display it in the app), you will see a screen_view event in the ‘app’ reports.
If the page is shown in the embedded browser of the app (e.g. you will see a browser pop up that loads the page) you will not get a screen_view event. You might be able to configure a custom event based on what is available (from the refresh/close sections of the browser) but mostly it will be a sandbox.
If you own the page that is loaded in the embedded browser and can install GTM tracking on it, then you can send the data through as a datastream which will appear in the web reports. In Explorer, you can bring in the page path, browser and user source to see the page views that happened within an app by filtering browser to contain “in-app”.