If you'd like to temporarily stop moving elements in your map, hit the spacebar. 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 to select all elements, then hit the pin icon in the sidebar. This will pin all existing elements in place.
If you'd like to set the default element movement behavior to "fixed", go to Settings, click on General, and change the "Default element behavior" from Floating to Fixed.