Sounds like your proprioception sucks. I had/have issues with scapula winging I sort of developed after an injury. Scap push ups work for me now, but they didn't for a long time because I literally could not activate them. Two exercises helped with that. One is simply holding a ridiculously light weight (like 1-3kg) and doing intensely focused protractions lying on a bench (or the ground). Make sure you maintain intense focus, do one arm at a time and hold the contraction for at least 3 seconds. Don't worry about weight, this is not a strength exercise. Force the protraction as hard as you can, try to touch the ceiling.
Another one that helped me is pushing against a wall with a tennis ball between your palm and the wall. Again, forcefully protect your scapula (try to force yourself away from the wall). With that arm, draw circles or an X to start out with. You could even write out the alphabet, though you will probably fatigue very easily initially. Im sure you can find some youtube videos if you can't visualise the exercises. These exercises with a high frequency (everyday at least, could progress to twice per day if you want, they are not taxing at all, though after the first session you should feel some soreness) for a few weeks should get you ready to progress onto scap push ups and all the strengthening exercising. Good Luck bro