The timeline functionality is active for the ticket which is In Approval status.
SAP Cloud for Customer.
Reproducing the Issue
Go to the Service work center.
Go to the Tickets view.
Search and open ticket id LMN (where LMN represent the ticket id, which is in approval status).
Open ticket LMN and go to the Overview facet.
Here you can see under Timeline section, the creating email and other functionality is still possible.
Not all the fields and actions are greyed out once ticket is send for approval.
Allowing to edit certain fields and actions even for in approval ticket is an expected system behavior.
Timeline , Ticket , In Approval , KBA , creating email , field , action , LOD-CRM-SRP-INT , Ticket Interactions , Problem