Also these guys in Canada offer 60- and 20-minute PCR tests: https://www.bonvoyagemedical.com/
Those are NAATs, which, while they are based on polymerase chain reaction (PCR), are not the same as PCR reported in the test. Plus, I'm unsure as to where you saw 20 minutes, the shortest I see offered there is 'whithin an hour'.
https://www.medicaldevice-network.com/news/fda-roche-pcr-tes...
Seems to be FDA approved.
While I have no clue how they work in detail they offer 60 min express PCRs in Germany at least at my airport.