Lead flux went away like 45 years ago. But sometimes galvanized pipe has some amount of lead in the zinc coating, and a mixed cooper/galvanized installation can accelerate corrosion.

Post-Flint, lead is the new asbestos. Because the standard is zero tolerance, there’s alot of noise on the topic.

PEX is great, but I’d personally always go for cooper if I could afford it. We tend to learn new things about plastic and risks over time.