Not consenting to a police search doesn’t stop the search, and that’s ok.

What it does is make the fruits of that search inadmissable, and may also enable you to sue them if the search was unreasonable or excessive, or the pretext violated your rights.

Even if you know you don’t have anything in your car, verbally and clearly say that you don’t consent to the search, and would like them to note that fact, but otherwise comply. Lots of people have been caught up by police planting evidence, and you don’t want to be one of them.

Figuring out the Parkinson’s linkage is challenging too, because glyphosate is just one of many chemicals used in agricultural settings. It wouldn’t be surprising for the correlation to be caused by another chemical with strong evidence of casual linkage to Parkinson’s that itself is correlated with glyphosate, like Parquat. (Since Parquat is a herbicide, places that used it may also use (or have switched to) glyphosate.) Totally worth continued scientific study.