Does anyone know a way of turning off the Week & Month sub-headings on a Folder by Folder basis. If it’s obvious please be gentle. 
In the new Kmail, to the right of search bar in the top, there are 5 buttons.
Hover the mouse pointer over each of them, click on one that says “Select Aggregation Mode”.
From the drop-down-menu select “Flat Date View”.
Thank you very much for that information. I never thought of looking at those buttons. 