wordpress performance problem

Best bet? Turn the crank faster… upgrade your server. Add a CDN and offload anything you can from the server to something else.

I found the reason. The site is doing version control. at first it does not test plugins. then start to test plugins. The site is slowing down when it checks the version of add-ons.

https://tr.www.ads-software.com/plugins/stops-core-theme-and-plugin-updates/

I used this plugin. it only conceals the writings. updates are running in the background.