Hi! Thank you for asking!
If you want to install Hide Singular title as multisite plugin, it’s recommended to use “must-use method”.
- Install WP-Autoloader as must use plugin
- Install Hide Singular Title as must use plugin or as regular plugin and activate it for each site manually.
Make sure that WP-Autoloader is loaded first of all of must-use plugins. Please read those instructions for more details.
Please read also WordPress Codex article Must Use Plugins for more details how to install properly must-use plugins.