Does anything clean the hardened part of artist paint brush?

Turpentine

I recently salvaged a brush by working Goo Gone into the bristles and then soaking it overnight.

Soak the brush overnight in hand sanitizer or rubbing alcohol. Remove the brush and work the bristles with your fingers to loosen and separate them. Rinse under water. Repeat if necessary.

Vinegar worked for me too!

I use the Masters brush cleaner. you have to let it soak , rinse and soak . I did not know about the vinegar... will try that

https://www.hunker.com/12000761/how-to-soften-paintbrushes

I purchased it at Preston's art center , Louisville Ky.. .They can do online ordering..But you can probably get it where you buy your art supplies. I know Hobby Lobby has it. It is called Masters brush cleaner and preserver. Cost is about $10 . Lasts quite a long time . It comes in a cake form and is used with water. You wet your brush then proceed to lather your brush... It reminds me of when my Dad used to shave with the old cake shaving soaps....