You open a landing page on your phone, start to tap "Get started", and the button jumps down because an image above it finished loading. That is a layout shift, and the usual cause on a marketing page is an image with no reserved space. What the sources say web.
Source: [Dev.to](https://dev.to/mercerk17/reserve-image-space-on-your-landing-page-so-the-button-does-not-jump-a-layout-shift-check-38ih)