If you are in doubt you can always put up another mounting board across the wall and attach the board to the edges of the wall... You can paint the added board to blend in with your paint scheme...
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Tapping on the wall should tell you what is behind the wall...
Some folks like to use these wall mounting screws that spread out behind the wall.… I don't recommend using the toggle type bolts as with those they will drop behind your wall if you remove the screw...
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Roy Ken