There are many ways to check what CMS a website uses to build a website. Examples are as follows:

1. Look at the background login path, as shown below, php

2. The WP, dede, and empire cms backgrounds that use PHP programs all use this kind of program. Now use the elimination method to guess what kind of program the following is. Obviously, anyone who has used WP and dede knows that their login interface is not like this

So, this cms must be the imperial cms.

Method 2:

Check robots.txt to see if wp-admin or wp-includes is blocked or not, which is obviously marked with wp.

You can also log in to your ftp account and check the domain name suffix.