Opportunity record > Activity/Communication tab > Create mode vs Edit mode shows different subtabs

1. Navigate to Transactions > Sales > Create Opportunities > List > Edit an existing opportunity record.

Actual Result in Edit Mode:

In the Communication tab, the following subtabs are displayed:
Messages, Activities, Files, User Notes

2. Navigate to Transactions > Sales > Create Opportunities.

Actual Result in Create Mode:

In the Communication tab, the following subtabs are displayed:
Events, Tasks, Phone Calls, Files, User Notes

The reason why Messages subtab is not displayed in Create mode for opportunity records is that the record is not yet set up. The system will not be able to send a message from a record that still does not exist. After creating and saving the opportunity record, this tab is available in Edit mode. In addition, other records like Sales Orders, the Messages tab is exposed in Create mode since it has a native functionality to email the transaction upon saving.