I hope you're not referring to the debunked "stairsteps" myth. The reason why the filter on the output of a DAC is called a reconstruction filter is because it reconstructs the waveform
exactly as it was before it was converted to digital:
If you're an adult male, you probably can't hear much above 15 kHz, let alone 20 kHz. Try turning on an old CRT television. Can you still hear the flyback whine? If not, then that means you're not hearing anything above 15.7 kHz.
And regardless, many vinyl records are mastered with lowpass filtering around 16 kHz, to keep high-frequency sounds from causing mistracking and splattering on turntables with a conical stylus.