How do I know if I have enough visitors?

When doing a PageSpeed Insights test, you will always see "Lab data". "Field data", sitting on top of "Lab data", will be displayed as well. When you don't see any coloured bar charts, your webpage didn't have sufficient visitors (yet) to yield any data.

However, if your origin (domain) did have enough visitors to yield a summary, PageSpeed Insights might at least still show you an origin summary. When no "Field data" at all is being displayed, your website or webshop doesn't have enough visitors and you won't benefit from Core Web Vitals ranking factor. Do note though that improving your pagespeed, performance and UX will still impact conversion and might make you future proof in case the amount of visitors increase over time.