I have it, both sides. Yes, it is awful.

Get physical therapy and have them show you how to do it at home. Since mine was out of pocket, I saw no reason to pay for something I could do with elastic bands while watching Sports Center. But....it takes a long time. Stick with it.

A couple of years later and I still do my exercises.

I had adhesive capsulitis before and after rotator cuff surgery some years ago. PT helped but Chiropractor was able to bust the adhesions. It took a long time and lots of pain. Right now, I am at risk of frozen shoulder due to small rotator cuff tear, broken scapula, and compound break of the clavicle from a crash 2 months ago. I know if my shoulder freezes, it can be remedied but it is a PITA. Getting second surgical opinion today.

So far, I haven't had a non-operable injury which I wasn't able to resolve using Dr. Google. I just checked and there's a plethora of offerings, thankfully mostly duplicating what's on other websites, so that's probably what one needs to do. I always push to the level of discomfort, not pain.

I think it was back in 2013 when I got a frozen right shoulder.
It took about 2 months of physical therapy, and the most painful PT I've ever had.
I haven't had any further issues with the shoulder for years.