Hi - just making sure. If I click MOBILE icon at the top and make changes, that will NOT Influence the Desktop site?
Or am I supposed to make a secondary Mobile site or create two duplicate layouts and HIDE one on Desktop and HIDE the other from Mobile?
Correct, changes made in the styles panel on the mobile breakpoint will not impact desktop (or any other above it). Changes cascade down from Desktop, so if you were to make a change on Tablet, that change would apply to Mobile Landscape and Mobile Portrait as well.
Check out the Webflow University article on breakpoints for a more thorough explanation.