I had a hard time finding how to add a boolean property. I expected to be able to add it at the top level of the variant group. I can see now why that might not be possible given the way it is structured.
One easier idea could be to use a different icon for it? I was confused that it was the same icon as “apply instance swap property” but a different place. I was watching tutorials and kept clicking the “apply instance swap property” one, thinking it was broken.