If you choose the ‘Routes’ option (with the little sign) then it’ll stick to cycle routes only.

Benn: as a learning exercise I explored RF's method (as I understand it), using the Android App; my notes as below in case they help you or others.

To get the full loop in one route, plan a route covering to halfway round the loop - say Newent to Bromesberrow Heath; tap on the "Routes" symbol as per RF, then on "Get route". This will create 1/2 the loop. Then with that route open, do a "long press"on the map somewhere about 3/4 round the loop - say Highleadon -which will bring up an option to "Extend to here" - select that; then v close to the start do another long press etc to complete the loop. Assuming you have created a (free!) CT account, you can save the route privately or publicly and load it into the app to give directions etc when you do the ride. (Note: I have saved a public route named Newent Loop part 1 which is just the first step).

I also tried doing this in the website - which has richer tools for route planning, so normally the best place to plan. In my CT account I have preferences set to allow "click to add via points" - so clicking on the map to extend a route works much as in the app. HTH