I see a green border on your screen shot. This is only visible to you when you're sharing a portion of your screen (a single window for example). It's meant to highlight which window you're sharing and can't be removed. Those you are sharing your screen with do not see the border. See Sharing your screen or desktop on Zoom for more information.
If my reply helped, don't forget to click theAccept as Solutionbutton so others in the Community may benefit as well!