Google measures three things about how a page feels to load. They appear in your monthly report.
Largest Contentful Paint
How long until the main content appears. Under 2.5 seconds is good, and it is usually governed by the size of the hero image.
Interaction to Next Paint
How quickly the page responds when tapped. Under 200 milliseconds is good.
Cumulative Layout Shift
How much the page jumps around while loading. Anything under 0.1 is good; the usual culprit is an image without dimensions.