How to Turn Off the Leaderboard and Crowns
From your mobile device:
To turn off the YouTube Leaderboard on your phone, exit the stream and go to your Profile Picture in the bottom right corner. From there, go to the cog ⚙️ on the top right. From there, scroll to audio/video preferences. There's a section that says 'Live Chat'. Click on that. There are 3 options. Click on the slider that says Live Chat Participation. It is OFF if the scroller is blue.
Video tutorial:
From your computer/desktop
To Turn off YouTube Leaderboard on your Desktop/PC, go to your Profile Picture on the top right hand corner of your screen. From there, on the menu that comes up, scroll down to Settings ⚙️. In the Settings Menu, on the left hand side of the screen, click on Privacy. Scroll down to Live Chat. Click the slider. It will be OFF if it's Blue.
Video tutorial: https://youtu.be/feYGgnHAXkY