You can follow these steps to hide the email mini compose in HR Agent Workspace
Ensure you select scope as "Agent Workspace for HR Case Management"
Steps below:
-> open this variant "Case SRP" and make a duplicate of that
-> Set details like this
-> Click on 'Activity Stream Compose' node
-> In Config section --> Expand Advanced
-> 'Show email mini compose'
-> use Static input -> Never
Earlier: Mini Compose Email is present
Output: Mini Compose Email is gone for HR table in HR Agent Workspace
