Source for once per year fish consumption? I couldn't find that.

You can't have it needed in some stuff and critically dangerous if it's a bio-accumulating chemical that virtually never breaks down. To reduce it enough to not be a hazard world wide you would functionally have to stop using it everywhere.

I haven't seen any definitive results on dangerous health levels, 4.4 ng/kg might be it, but then other studies show people with mg/L of blood concentration. Overall the effects of exposure seem to depend on more than just the concentration, such as health status, exposure duration, magnitude of exposure, and how lucky you got with the genetic lottery. Even then we are fairly certain it is bad, we just don't know what or how specifically. I would also throw caution at any study using ng as a serious measurement here, especially over prolonged exposure. The problem with measuring on such a low level is that you have far too much uncertainty to claim any true accuracy, at best these studies are guessing when they throw out numbers. Hell, the EPA just came out with a standardized method for analyzing PFAS last year.

At those levels of exposure you're probably getting it just from eating commercially grown fruits and vegetables, because it can bio-accumulate in those as well.