Brett

Frontend Features: 
 – adds a toolbar to the bottom of WordPress pages that will show meaningful information that helps developers to create optimized WordPress sites. 
 – Info includes SQL queries, query vars, peak memory usage, and a filetrace.
Backend Features: 
 – Provides a very basic checklist with suggestions for development. 
 – Shows basic server stats and information 
 – phpInfo 
 – WP rewrite rules (coming soon)

Developer Toolbar

Adds easy to access data for developers, including a fixed toolbar to the bottom of pages that shows query data and memory usage among other data.

activity-log.com

Plugin allow you to run most important test for performance: request time, number of database queries, memory usage
You will be able to detect plugin which cause troubles and result with longer waiting time for request results
Testings are executed based on your homepage
<iframe loading="lazy" title="WordPress Profiler – What Slowing Down Your WP" width="750" height="422" src="https://www.youtube.com/embed/3hJbClFbw5s?feature=oembed" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe>
How to use it?
In Dashboard go to Tools->Profiler What Slowing Down
Click on run test on all plugins (first link) and then near wanted plugin, run few tests and compare results
If you get significantly lower results, means that this plugin causing slowness
Hint: Lower numbers are better, means that page load faster without this specific plugin

Profiler – What Slowing Down Your WP

Plugin allow you to run most important test for performance, request time and number of database queries With this Plugin Performance Profiler you wil …

Developer Toolbar vs Profiler – What Slowing Down Your WP