My layout for the FoldKB has three layers:
A default standard QWERTY layer,
a second "programming" layer with
a third "mouse" layer with mouse keys on the right half. No special functions have been added to the left half for this layer (yet).
This was written for a FoldKB with one encoder, and that is made to function as a mouse scroll wheel on all layers. Pressing it is a mouse left click and shift-pressing it is a mouse right click. (Presumably both encoders would do the same thing on a FoldKB with two.)
The backgound lighting levels indicate the layer: dimmest for the default QWERTY layer, middle brightness for the mouse layer, and brightest for the programming layer.