Activity button (Fenix 6 Pro Solar)

I noticed the activity button (top right button) on the Fenix 6 Pro is different then all the other buttons. It looks like it has a screw ring around the button and it is colored blue. Anyone have an idea why and what it is used for? Looks like you can spin the crew ring, but I'm not seeing any effects on the button being pressed or on the watch electronics itself.

Thanks

Alain