Degraded WordPress admin dashboard performance [closed]

Install the Query Monitor plugin if you can.

This is the most powerful WordPress debug plugin that can show all the issues including what is taking how much time to load.

Query Monitor Screenshot

Once installed and activated, this plugin shows on the top bar, both on the front end and the admin panel. Once you click the bar, it can show you all sorts of necessary information to debug possible issues.

You may also want to read the documentation about debugging in WordPress.