If you'd like to temporarily stop moving elements in your map, press the spacebar on your keyboard. Press spacebar again and they will go back to floating.
If you'd like to permanently stop all elements from moving, you'll want to pin elements in place. Do this by pressing A on your keyboard to select all elements, then click the pin icon in the left side panel, or press P on your keyboard. This will pin all existing elements in place.
For more information about layout options, or to set the default element behavior (fixed vs. floating) check out the guides on the fixed layout and force-directed layout.