Hi how are you?
You can use Power Automate with the CDS Current Environment connection to run a flow when a new email message is created regarding an incident and send the email to the case owner.
Create a new flow using the connector Common Data Service (current environment)

Select the action trigger "When a record is created, updated or deleted"

Set the properties like below and after click on the 3 dots of the trigger and click in settings

On trigger conditions add this one @equals(triggerBody()?['_regardingobjectid_type'], 'incidents')

This wil tell to flow to execute only if the email created is regarding an incident
After that add the action to create a new email message adding the owner of the incident on the activity party list and is done!

Please let me know if this answer your question. If you have doubts or concerns please let me know.
Regards.
Rodrigo Hentz
Microsoft Support Engineer