See also
https://medicalxpress.com/news/2024-02-danish-drug-chemicals...
for a drug that appears to lower PFAS levels. I'd be concerned about where the PFAS is partitioned in the body: giving blood isn't going to make a big difference if most of the PFAS is in your fat.
If you go regularly the concentration of PFAS in your donated blood would be lower compared to going more sporadically.