I think the most alive folk music is the one from górale (Tatra highlanders). It's very distinctive, after 2 chords you know it's from them. https://www.youtube.com/watch?v=-G2qaeoQ4po https://www.youtube.com/watch?v=b7o-Mh_ang4 https://www.youtube.com/watch?v=sOCTwL14-T8
Besides górale there are a few folk songs that everybody knows and sings at campfires or on weddings or other gatherings (they are called "piosenka biesiadna" because you usually sing them when you're eating).
Examples: https://www.youtube.com/watch?v=D1q0-bT6H7s https://www.youtube.com/watch?v=wug2YJGqca4 https://www.youtube.com/watch?v=YjY88qmsbDg
I'm not sure they are 100% authentic folk music though, because most versions nowadays are disco-polo :)
Example of true folk song I've heard a few times in my region (on weddings or concerts): https://www.youtube.com/watch?v=4bY7J3KTx1w
It's in regional dialect that nobody really speaks anymore in daily life.
Another kind of folk music that's still alive is przyśpiewki (orchestra plays same tune and people switch and sing to diss everybody else on weddings :)). It's basically folk rap battles :)
Example: https://www.youtube.com/watch?v=mDABYBOXaAg
BTW in one Kaczmarski song there's a Russian folk song included. I always wondered if it's true folk song or something he invented. Have you ever heard it?
The inner song starts here: https://youtu.be/7cxciyZEBkE?t=151