you eat fungus spores every single day nonstop. They are everywhere. Just cause this one eats plastic why would the spores be dangerous? (also it probably only eats one type so like 5% of plastic)

Theoretically if they don't produce toxins as a byproduct of plastic metabolism, eating the plastics out of our brains could (in an idealized and highly unlikely case) be a good thing. If they don't also eat organic matter they'll starve out when the plastics are gone and our immune system could clean out the debris left behind