Add New Permissions for Subscribe and Unsubscribe

The form class where you use these new permissions already is guarded by a permission. Please explain what purpose would allow access to the form but not allow the user to use the form.

Indeed, you are correct that there exists a permission to access the form. Nevertheless, in cases where there are multiple user roles, it is imperative that not all users have the capability to subscribe to the content. In this scenario, the site administrator should have the privilege to subscribe, whereas the editors should only possess the ability to pull updates.

Currently, I am utilizing entityshare to distribute content across 13 different sites, and my intention is to restrict the number of subscriptions.