On a given node, we want an authenticated user to be able to click a link to subscribe to the item and any time that content is updated or a comment is made, the user who subscribed is emailed with an update.
I have attempted to implement this functionality using Rules and Flags, a solution which would be easily constructed in D7. However, although I have a flag for subscription set up on the desired content, Rules in D8 seems somehow unable to handle emailing a list of users who flagged this content upon update or a comment being made on it.
Yet I must be missing something because over 10,000 sites are using Rules for D8 and surely many are using more complicated functionality than this.
Question: How do I set up Rules to send an email to all users who flagged a piece of content in D8?
Follow-up: Is it that this is not possible? I have read that D8 Rules cannot yet handle custom fields because that requires the condition 'entity has fields' which doesn't work in D8.
Details: Using Drupal 8.5.3, Rules 8.x-3.0-alpha4, Flag 8.x-4.0-alpha3