Why does GA4 show page views but zero engagement time?

That usually means GA4 is getting the page_view, but it isn't receiving usable focused-time data. A page view fires when a page loads or its history state changes, while engagement time comes from engagement_time_msec and only counts time with the page in focus. So a very quick visit or a background tab can legitimately show a view and 0 seconds.

If it's happening across almost everything, test a real visit in DebugView and look for user_engagement or other events with engagement_time_msec. Also check whether page views are being sent through Measurement Protocol or a custom setup; Google says those events need that parameter for accurate engagement metrics. Don't add a fake timer just to make the report look better—make sure the browser tag and intended events are actually firing.