Getting your arms properly overhead is the thing people most often tell me they simply cannot do, usually while blaming a joint that is not responsible.
The ribcage moves too
Raising an arm overhead is not just a shoulder action. The shoulder blade has to rotate across the ribcage, and the ribcage and upper spine have to allow that by extending.
If your upper back does not extend, and for most people who work at a desk it does not much, the arm runs out of road early. The joint then finds the remaining distance somewhere it should not, which is why the lower back arches and the ribs flare every time somebody reaches up.
The shoulder was never the limit. It was the part that ran out first because something else did not participate.
How to tell
Stand with your back against a wall, heels a little away from it, lower back in its normal shape rather than pressed flat. Now take your arms overhead and try to keep the ribs down.
Most people lose a lot of range. That gap is the honest measure and it is information, not a verdict.
What actually changes it
Upper back extension work, which is slow and boring and works. Time spent over a support, thoracic rotation, and any of the positions where a teacher spends an irritating amount of time on where your ribs are.
This is a large part of why I hold things for so long and talk about apparently irrelevant body parts. The relevant body part is frequently not the one that hurts.
What to stop doing
Forcing the arms back with momentum, and any version of yanking. You will simply take it out of the lower back, which is what has been happening already.
The timescale
Months, not weeks, and it moves faster than most people expect once they stop working on the wrong joint. Shoulders that have not gone overhead cleanly in twenty years do not resolve in a fortnight, but they do resolve.