To change keyboard shortcut for show/hide results pane, go to Tools > Options in SQL Server Management Studio:

Navigate to Environment > Keyboard > Keyboard.
Search for “Window.ShowResultsPane” using “Show commands containing” textbox.
In the “Press shortcut keys” textbox, press Cntrl + R buttons on the keyboard at the same time.
Click the “Assign” button and then click “OK“.

You might need to restart SQL Server Management Studio to apply these changes.