F-Droid has a few options. Just search for interval or HIIT.

I have found this video helpful for my upper back and shoulder pain. He also has a shoulder impingement video where he mentions scapular stabilizers that might be more helpful for your needs but I haven’t tried that one.

If you’re using an app, you may need to adjust image quality in the settings. I thought the same thing until I tapped the HD button in Boost.