Any modal content blocking the page content viewability and that triggers automatically without user interaction, are counted as Intrusive Interstitials. For example, your site has a popup that shows up on screen after a few seconds, but on mobile it covers the entire screen. Thus blocking the page content or dimming with grey background. You can read more here- https://www.searchenginejournal.com/counts-intrusive-interstitial/180023/
We can use cookie consent popups or notices like that but it should be responsive on mobile and should not block the entire content of the page.