Most of the things you hear about Kary Mullis are internet fake news.
Comments like, “Kary said you can’t use PCR testing to detect viral loads” or “Dr Mullis said that this PCR test was not made to detect any type of infectious disease.” are straight up lies and misattributions.
He didn’t say PCR testing couldn’t be used for testing for any diseases, as some social media posts claim. Confusion seems to have arisen from quotes of his in a 1996 article about HIV and AIDS. In this, neither the author of the article, nor Dr Mullis said PCR testing does not work or only identifies the DNA or RNA of the person being tested.
The author actually quotes Dr Mullis as saying “Quantitative PCR is an oxymoron” within the context of testing viral load (the amount of virus present) in people with HIV. This doesn’t mean he thought PCR testing didn’t work at all, but that there are limitations in detecting the specific levels of a virus from a sample using PCR testing.
Fact checkers at Australian Associated Press say that when the quotes about PCR testing picking up the DNA of the person being tested first appeared online, they were “not attributed to Dr Mullis but to an online commenter called "VirusGuy"”.
Kary Mullis would have most likely taken covid-19 very seriously and would have supported his tests being used to detect covid in others. People who think covid is some sort of a hoax have been promoting this guy like crazy but lost quotes online of his aren’t actually his quotes, and furthermore her would have laughed at the “covid is a hoax” crowd would he have lived today.