Blood donation helps the donor, but what happens to the recipient? Would it not be possible to accumulate PFAS in your blood stream by receiving PFAS-concentrate blood? Is it that simple?

Yes, but since blood donations are not tested for this you don't know what you get so people are already getting PFAS contaminated blood.

You could just do phlebotomy (blood letting) where your blood is discarded in case you have insanely high PFAS.