Do all sound bars have mounting holes?
Not quite. A Sonos playbar mount is required. It has particular nipples on which the sound bar is held. You might be able to be creative and use the holes that would fit into to hold the sound bar if you could have the right hardware.  However, it really is probably not a great idea. Simply place the soundbar on the base & adjust the extended commands to clip the soundbar for soundbars without holes drilled.