Cycles are copies of the particular strand of nucleus acid you are testing. It’s an exponential tests so 1 cycle makes 2 copies of the nucleic acid, 2 cycles makes 4 copies, 3 cycles makes 8 copies, 4 cycles makes 16 copies, etc. At 35 - 40 cycles, you are literally making billions of copies of nucleic acid and you are bound to pick up just about anything including fragments of nucleic acid which will give you a false positive. That’s why Kery Mullis (inventor of the PCR Test) stated it should never be used as a clinical diagnostic tool. Interestingly, he just happened to die in 2019 right before the rona hit the market!