Tracking Page Scroll depth means tracking how far people scroll down each page on your website. This can be useful in determining whether or not visitors are seeing some content that may not be visible unless the user scrolls down the page.
1) Use the Heatmaps and Session Recording Plugin
If you’re using the Heatmaps and Session recording plugin for Matomo then you can automatically track how far people are scrolling down the page by viewing the heatmaps for those pages in Matomo if you have a heatmap setup for those pages.
You can find out more about using Heatmaps in our Heatmaps and Session Recording User Guide
2) Use the Matomo Tag Manager to track scroll percentage.
See our FAQ for step by step instructions: How do I track Page Scroll with Matomo Tag Manager?
The way you implement this on your website will be entirely up to you, but you could use this Stack overflow question for some more information on how to achieve this.
_paq.push(['trackEvent', 'Scroll_depth', '25%']);
You will need to track an event for each different scroll depth you would like to track on your website.
You can learn more about tracking events in Matomo in our Event Tracking User Guide