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

https://instanceName.service-now.com/now/builder/ui/edit/experience/8ad40be90fe120102208555db4767e7b...

-> 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