That button is magic, but unfortunately, it doesn’t work in this case. I should have clarified this part:
I’m trying to mass select the same layer within hundreds of separate variants to then apply the layer boolean property.
To be specific, I’m trying to make a customized version of the Phosphorus icons where the “DuoTone” layer in each variant set is a boolean toggle instead of a whole variant. My goal is to make all “stroke” versions (Light, Regular, Bold) have the DuoTone layer as a boolean option.
You can create a variant property named Due Tone then select all due tone Icons and set the value True, while settings other to False. This will make the property variant as Boolean.