When applying a mask for no data to a raster symbology, you first need to tick the box that says "Display background value" Then there are the 3 RGB values you need to enter to make your no data transparent or what ever color you require. This is mostly 255, 255,255 for white back grounds. When you tick the box and start entering the values, Arc loads the symbology after each value and you have to wait between 5 and 10 seconds for each entry before you can continue to the next value.
A good idea would be to enter the values before first ticking the box. Once you have entered your 3 values, then you tick the box and Arc only has to recalculate the symbology once.
Arc version ARCGIS Pro 3.02
