It sounds like you are nearly there OP. You’ve got an undeniable problem that you can easily demonstrate to your shop. A good shop will be able to fix it straight-away once you show them what you’ve discovered. And you can verify the problem is fixed, the same way.
MM64, you’ve “hit the nail on the head”. In light of the work that’s been done already, that’s all it could be.
Congratulations.
With the dragging wheel in the air open the bleeder on the caliper (if the bleeder is rusted shut loosen the hose to caliper bolt until fluid comes out) . If that frees up the wheel you have a hose or rarely master cylinder problem.
If you change the hose you’ll also have to bleed the brakes. Sounds like this is new to you, I’d have a pro do it in that case.
The caliper may have to be lubricated, these things "slide’ in and out, could need some light lube. Rocketman