If you need a permanent free solution, several "gain rider" plugins mimic the automatic fader-riding technology of the Waves version:
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Set a compressor on your music bus and route the vocal as a sidechain input to automatically dip the music when the vocals play. If you need a permanent free solution, several
If you can’t get Vocal Rider legally for free, consider these free (or very low-cost) alternatives and workflows: Download Vocal Rider Plugin Free