On the Samsung smartphone, the button grid refers to the quick settings in the status bar. Just like the app overview or the start screen, the grid can be adjusted to 3x3, 4x3 or 5x3.
For example, the 5x3 grid can be used to display a full 15 quick settings. The size of the buttons also changes depending on the selected grid.

Android 10 | One UI 2.0
Button Grid -  Pull down the  Notification bar
Button Grid -  Open the  menu
Button Grid -  Tap on  Button grid
Button Grid -  Choose desired  Grid
Button Grid -  Confirm with  OK
  1. Pull down the Notification bar
  2. Open the menu
  3. Tap on Button grid
  4. Choose desired Grid
  5. Confirm with OK

Samsung Instructions