All audio amplifiers have high frequency phase shift so they need a frequency compensation capacitor to roll-off the high frequencies so that there is no voltage gain at a frequency with enough phase shift to cause the negative feedback to become positive feedback and cause the amplifier to oscillate.
Therefore the open-loop gain of the amplifier is reduced at high frequencies which caused distortion to increase at high frequencies.
You can either see the distortion in a simulation or you can build a prototype and measure the distortion. Sometimes the simulation is wrong.