There is a lesser known piece of information that can be defined in the plugin header that tells WordPress to only show the plugin on the WordPress Multisite Network Plugins page. This will hide Pressbooks plugin from being displayed and activated at the site level in WordPress Multisite. To only allow Pressbooks to show at the Network Plugins level.
adding this one line to Pressbooks header code:
Network Only Plugin Header:
Plugin Name: Pressbooks
Plugin URI: https://pressbooks.com
Description: Simple Book Production
Author: Book Oven Inc.
Author URI: https://pressbooks.com
Text Domain: pressbooks
GitHub Plugin URI: https://github.com/pressbooks/pressbooks
Release Asset: true