When keyboard is on..it won't work..rest, while taking screenshots, your palm should touch the edge of your device.. or you can try one hand operation+ or Accessibility>Interaction and Dexterity>Assistant menu feature or As your device is note 10+, then use edge panel/softkey edge Or Use Goodlock app/NavStar
Thank you very much, I already figured it carlyer. Side button, BIXBY, Eadge Panel option, spen command I can do those, Problem was about Palm gesture . Then I Figuard it's not some motion gesture , I have to touch the screen by using edge of my Palm. It's Something like 2finger Or 3 finger Gesture Like Other Phones. But thank you Very much. Your effort is most appreciated.