Wordpress - Add Wordpress MU Network Admin via Database

So, it turns out that those three changes were all that were needed. It also turns out that if any of the serialized arrays are modified incorrectly (which is easy to do when modifying them by hand), the system will just assume you are not a network administrator.

Correcting the serialized array for the site_admins option fixed the problem.

If you can connect via SSH, you can also add super-admin rights to existing user with WP-CLI by running command wp super-admin add <username> on the server.

As you are running a copy of the website in your local machine. Open your terminal, install WP-CLI globally and once it's installed, go to your website folder and type: wp super-admin add <username>.

I hope it helps.