when a task is done

hello

I am trying to inform every member of my plan that a task is done.

But, I can only find "send to the group". But my Group is made of private channel and I don't want everybody to know. Only the members of the plan. 

Does anyone have found a solution so every member receive an email ?
I tried with power automate but I have to enter the adresses. I need it to be automatically done because my plan will be copied again and again, only the members will change.

Thank you for your responses