Is this plugin working on WP Multisite?

Yes, this feature is available for Hide My WP Ghost.

It works with both structures of WP Multisite: subdomain & subdirectories.

Hide My WP Ghost works on WP Multisite and you will configure it for the entire network.

Multisite counts just as one site. Because the settings and usage will happen in Network > Plugins, and not on each individual site.

The Ghost version also works with Apache, Nginx, IIS and LiteSpeed servers.

You can see all the features here: https://hidemywpghost.com/hide-my-wp-ghost-security-features/