I’m still not able to reproduce this, and I would like to make sure it works for others! Can you please contact me (crx@pfish.zone) so I can figure out the problem?

Sorry that the extension doesn’t seem to be working for you. I can’t reproduce this issue; for example, when I open GMail, the little icon is hidden. Since many of the CSS changes we do are identical, I would either extension to work roughly as well as each other (though I think there are slight differences between what we catch; for instance they use a method of hiding the "summarize this file" menu item that is a little too fragile for my taste). Could it have been a matter of needing to refresh the page?

The Gemini buttons that appear in a new Google Doc unfortunately can’t easily be handled by either of us (i.e., the ones you see when you create a doc with https://docs.new); those are not HTML elements that can easily be hidden with CSS, and instead are drawn on the page as if they were images.