The PageSpeed Insights tool from Google is a great way to quickly get actionable insights about where to improve your website and app's Performance, Accessibility, and SEO.
To see how your public site or app does, grab its URL and analyze it at PageSpeed Insights.
It will take a minute to run on either Mobile or Desktop (make sure to check both) and then will output four headline numbers (out of 100) for each of the categories.
You can then dig in to each category to see what recommendations they make for improving your score.
This can also be run directly from Chrome devtools which is useful if you want to see how a locally running site is doing. You can run the analysis from the Lighthouse tab of devtools. Note: if the Performance score looks bad, it might be that you are running a non-optimized dev server that isn't reflective of how your site would do in production.