I've attached a screenshot of a handy feature of the classified symbology tab (albeit for ArcMap - I'd guess Pro has something even better), at the bottom right of the window you can see a feature count when you click on the break value.
If that's no good, you could reclassify the raster according to those breaks, then build or use the raster attribute table which will have the counts for you. I'd definitely build full statistics before and after.