It’s possible. I haven’t looked at the code. They aren’t using glob because word didn’t work. Is there a way you can add #blah to your calendar events? That’s how it seems to search for items, based on tags. I don’t use the integration and I haven’t really setup my calendars. So it’s hard to tell.
I would suggest checking out these recipes: Calendar - Home Assistant as examples for automations that can apply arbitrary logic to different event fields and not using the google calendar search. You can make a template binary sensor if you still want an entity.