Yeah it’s a “shortcut” to whatever the “main action” is of the interface you’re currently on. There’s literally no reason you couldn’t add this to the previous watches, since it’s just an extension of AssistiveTouch.
Just look at the video, clenching and pinching to navigate the screen. Video is from 2021, so it’s obviously not the Series 9 watch.
Here is an alternative Piped link(s):
https://piped.video/watch?v=2YduyTzZews
Piped is a privacy-respecting open-source alternative frontend to YouTube.
I’m open-source, check me out at GitHub.