PFAS are hydrophobic molecules so, not knowing what to do with it, your system will store them with the fat (also hydrophobic). Doesn't do much in itself (depends on the exact molecule though) but the issue is bioaccumulation and amplification: imagine the food chain as a large hopper, sprinkle a bit of none biodegradable shit on top and imagine the dose you get at the bottom of it. In larger quantities you start disrupting processes in the body often leading to cancers or a myriad of symptoms caused by endocrine disrupting.

Edit: commented before watching your link, there's slightly more to it but that's the gist yup