On Samsung devices with Android 10 and above, the Edge Panels is activated by default. A narrow black bar is displayed on the right or left edge of the screen that can be dragged into the screen. This opens the side panels. Those who don't use them can turn the Edge Panels on or off in the display settings.

Android 10 (One UI 2.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Display
Step 3:  Tap on  Edge screen
Step 4:  Enable or disable  Edge panels
  1. Open the Settings
  2. Tap on Display
  3. Tap on Edge screen
  4. Enable or disable Edge panels

Samsung Instructions