What this tile shows
Squizzie calls this one Largest Contentful Paint. It reads as a figure to two places, because rounding it to whole numbers would hide the movement worth seeing.
Where the number comes from
Google PageSpeed Insights. Site performance scores, Core Web Vitals, and actionable recommendations.
What you need for it to appear
PageSpeed Insights switched on in the Google Integrations hub.
The fuller picture
This is one figure out of a bigger subject. Your PageSpeed score, minus what isn’t your fault covers it properly.