Initially, the admin panel home was not loading. But got that to work by adding a line of code in a php file. But it did not solve the main issue. I still can’t access any of the menus and options. A circle spinning animation just keeps on going. I have tried renaming the themes and plugins folder to temporarily disable them, but it did not work. https://imgur.com/a6EdVpm
A clean, fresh WordPress installation would work. So something has changed or been added here to break this. You said you removed themes and plugins, that’s a good step. Do it again, and also remove any .htaccess files present in your root directory and wp-admin directory. 403 and 500 errors are often caused by misconfigured or broken .htaccess files, respectively. Also, if you used a particular security plugin check for .user.ini in your root directory and delete that too. Also that spinner is not a standard WordPress spinner afaik, so perhaps not all your plugins/themes are disabled.