Oh, I see what you are trying to do.
I think you are correct about knobs only working at the top level. I also would like to be able to swap knob functions in and out using groups. If you file a Feature Request on this I’ll vote for it.
The SD+ Touchscreen support is distinct from the knobs in that there is a “Touch Screen Configuration Group” item (found under the Stream Deck + part of the menu) that you can add at top level. This is a bit like a group/folder, but you can define a set of things to go on the touch screen in one of these and they will all be activated/display together.
The semantics of “Touch Screen Configuration Groups” are a little strange, because there is an Open trigger, but no Close trigger. (This seems like it could be improved!).
See Behavior of Activate Stream Deck+ Touch Screen Configuration Group?
(Not sure that the behavior remains the same as it was when I started that thread, but have a look…)
I think maybe there are not that many BTT users who have SD+ and SD Neo models, as the amount of discussion around features specific to these models isn’t very high…