Cumulative Layout Shift (CLS) refers to unexpected change in the position of content on a page, and usually happens because resources are loaded asynchronously or DOM elements get added to the page above existing content.
CLS can be problematic if it occurs in the instant a user wants to interact with an element on the screen, which might cause them to click or press something else.
But is CLS relevant during page load? In the time before the page becomes interactive, can a shift in the page's layout lead to a bad UX?
I am referring to the case where the user will see a spinner as well as potentially a dark overlay over the page, so they are unlikely to be trying to interact with the page. While the problem described above may not happen, I am wondering if CLS may still cause confusion due to elements momentarily being rendered in a location which is not their final location.