Add an element the uses variables into that frame. Or add a fill / stroke to the frame itself. Once there is something that is bound to variables you will be able to apply different modes

This is the layer panel that I don’t have.

I created all color variables and selected the frame, still no layer panel…

Ok issue solved.

I created the dark mode to the original/primitive color variable collection and the mode icon shows up on “appearance” panel instead of “layer” panel.

(adding dark mode colors to the alias collection using exiting variables from primitive collection does not work though)