I had a minor case of TOS after a double mastectomy. With PT, and other exercises I found it greatly improved. I havent had much issue with it, but have great sympathy for those that struggle with it. Thorasic outlet syndrome is quite awful if you cant find some relief.

I would stand just before a door way. place my hands on the jam (palms at shoulder level) and lean into the doorway. Feel all those muscles and vessels open up. dont push, just lean, allow a nice long stretch. put hands up higher or lower for a wider area of stretch. Felt so good after being tight for so long.

I hope you feel better.