The extension will register if they leave/join the meet (i.e., their avatar appears or disappears from your screen). But, it runs on only your computer so it does not know what is happening on the students' screens. To gather that info, you would need something running on their devices which would require a massive development and testing effort to ensure it works on all devices and OSs. If you could make it work, IMHO it would be a horrible invasion of their privacy... not a can of worms that I'd want to open