Why are email notifications not being sent when an Opportunity is shared with a Group?

Issue:

When I share an Opportunity with a Group, members in this group do not get an email notification with details of the shared opportunity.

Cause:

Only in-app notifications are supported when users share an Opportunity with a Group, and therefore, no email notifications are sent.

Additionally, the person who shared the Opportunity and is part of the group will not get the in-app notification, but everyone else in the group will.