When you open Administrator Backend, you see Warning Internet Explorer.

This warning can occur when you restore web from server to localhost on XAMPP, or after upgrade/update version Joomla 4. Some files *.css.gz and *.js.gz may be not load.

You need stop .htaccess, by rename .htaccess to htaccess.txt
Then, reopen browser go to Administrator, refresh webpage. 

Remember rename htaccess.txt to .htaccess when you finished it.