When selecting text and trying to use OpenType features using a variable font in InDesign I noticed that the little OT icon shows ‘OpenType properties are not applicable’.
Not the most obvious of nomenclature since all the fonts (static and variable) are presumably OpenType fonts.
I can’t reproduce this with any of the fonts I have lying around as both variable and static fonts – the OpenType icon works equally well for both in my InDesign.
Have you checked your variable font in FontGoggles or similar to make sure the OpenType features are correctly exported?