I did find this...
https://www.thejournal.ie/factcheck-pcr-tests-irish-video-5304097-Dec2020/
“You get a lot of false positives because you start to identify things that are nothing to do with the current infection,” Dr Carroll said. “It might be fragments of DNA from other coronaviruses.” This happens because the original sample is amplified “through too many cycles”, he added.
Dr Carroll, who has a master’s degree in public health medicine, says that a positive PCR test does not correspond to an active case of Covid-19.
Experts in PCR contacted by TheJournal.ie viewed the 97% figure for false positives as a misunderstanding.
“This is not true. This demonstrates a clear misunderstanding of the PCR primers,” says Michael Mina, a professor at the Harvard T.H. Chan School of Public Health.
Primers are the reason why the PCR test for SARS-CoV-2 will only pick up that specific virus and not any other coronaviruses.
“When setting up a PCR test, you need to know what you are looking for, otherwise you won’t amplify anything,” says Dr Cillian De Gascun, director of the National Virus Reference Laboratory in UCD.
Verdict
The video is wrong that the PCR test for SARS-CoV-2 gives a false positive rate of 97%. Also, PCR tests do not wrongly confuse genetic material from other viruses with SARS-CoV-2.
The scientific consensus is that PCR tests are the best option for public health screening right now.
Dr Cillian de Gascun of the National Virus Reference Laboratory in UCD says the actual false positive rate is between 0.1% and 0.2%.
As a result, we rate the claim that PCR tests have a 97% false positive rate as FALSE.
As per our verdict guide, this means: The claim is inaccurate.