SlowFinder

SlowFinder measures where your site spends its time during a front-end
request and attributes that time to the plugin (or theme, or WordPress core)
responsible for it.

During a profiled request the plugin wraps every registered hook callback in a
lightweight timer, records each callback’s “self” time (excluding time spent
inside other callbacks it triggers) and the database queries it ran, then maps
the callback back to the plugin that defined it using PHP Reflection. Results are
averaged across samples and shown as a ranked table with bars.

Two ways to run it

• Automatic — the site makes background (loopback) requests to the page for
  you. Fastest, fully hands-off.
• Manual — the plugin sets a short-lived cookie in your browser and you open
  the page yourself. Because it profiles a genuine visit from your real browser,
  it works even when Cloudflare bot fighting mode, “Under Attack” mode, or a
  hardened host blocks automated loopback requests. No server-to-server request
  is made.

More info: https://slowfinder.com