Is it possible to create a button (or other function) on the Task page where:
- User clicks button
- Email Global Action (or equivalent) launches on screen
- Ideally the To: field will populate with the Email of the WhoID for the Task
- When user sends email then update Task Status to Completed, Task Type to Email: [Subject of email], Comments to [body of email], and Due Date to today.
I'm shocked this isn't a standard function, or maybe it is and I can't find it.
Eric Praud (Activ8 Solar Energies) 
Forum Ambassador
I never even thought of this scenario :)
One thing I can think of is to create a screen flow with mandatory email fields (To address, subject, body). You can then add a Send email action to the flow after the screen and an Update record element to update the task you're on (you will need a record variable called recordId, spelled exactly like that, all in lower case except for the I).
You can now add a Quick action to the Task object and select the screenflow.
I've never tried this, but it should work, however, I don't think you can pick an email template this way, however, you could use some Text Template elements to create some templates users can choose from maybe in a drop down first, then the Body field could default to it
