I’ve used a product called Brush Plus to remove dried acrylics from brushes. There are several cleaners on the market that will remove the dried paint. Sometimes it take soaking them overnight in the solution. When I soak overnight I don’t put the ferrule or handle section in the cleaner. I thoroughly coat the brush strands then sit it sideways in a shallow dish with the solution. This helps keep wooden handles from absorbing the moisture.

I have used several brands of these cleaners and do find that some work better than others. Read the directions for removal of dried paint, too!
carly