Follow the steps below to create a Google Analytics Scroll Tracking Report in BigQuery:
Step-1: By default, GA4 tracks only 90% of vertical scroll events (via the enhanced measurement tracking feature). You need to set up custom events using the Google Tag Manager to track other scroll depths (like 10%, 25%, 50%, and 75%) or horizontal scroll tracking.
Step-2: Once you have set up scroll tracking and collected at least a couple of days of data, navigate to your GA4 BigQuery data table and run a query to check how the scroll events are being recorded and what event parameters are being passed along with this event type. This will give you a good idea of what scroll-tracking data to extract.