Polygraphs have been long debunked as pseudoscience. That's one of their not admissible in court
that is a simplistic view and why they are still used by the CIA and other agencies.
Lying takes much more effort than telling the truth. A polygraph can detect stress, not the same as a lie and certainly doesn't explain what the lie is, but the effort to beat the polygraph can overwhelm a good liar.
What really does work is micro expressions, vocal stress analysis, and someone who is very well trained in questioning techniques. Also the reason they will question people for 24 hours is to get them exhausted, again trying to overwhelm a very good liar.
So although they don't care very much about the results of a polygraph they will still use them. So saying they have been "debunked" is too simplistic. A polygraph does not tell me if you are lying or telling the truth. But people who can tell with a very high degree of accuracy can tell you with a high degree of accuracy if you are lying or telling the truth will still use polygraphs as one of many tools.