Is WAVES Harmony plugin compatible with MAC Sequoia 15.2?

I bought the WAVES Harmony Plugin for GarageBand. When set to produce a 5th above harmony and then applied to a prerecorded vocal track of a single voice the resulting harmony is off-key and robot-sounding. The source voice is on key with no need for pitch correction. I have tried adjusting every option which either makes it worse or does nothing to get an on-key human-sounding harmony. Is the plugin not compatible with Mac Garageband as it claims? I only want simple 3rd above and/or 5th above harmonies. After 20 hours of attempting to get them and failing, I am seeking help.

Thanks.