Jake, below are your two exercises. Do them as frequently as you need to. Your goal is to be able to feel the burning/activation in your mid/lower traps for 1 minute in both the below positions.
There is more we can do to strengthen, but for now, getting the proper muscles activated is key. This will be the foundation for your future exercises and movement patterns.
As a reminder to help connect the dots: your major issue appears to be that the muscles around your scapula aren’t doing the job to properly stabilze and move it. This results in an over-active posterior cuff musculature and hypermobility in the shoulder (glenohumeral) joint.
If you have any questions, use the discussion board below.
Things to remember:
don’t do anything that irritates the shoulder or causes pain—including exercises and reaching overhead.
When reaching overhead, keep the elbow bent to shorten the moment arm and reduce toque/strain on the glenohumeral joint