I signed up with fake name, delivered to a friends address, and a Privacy.com single use credit card. No one is forcing you to use real credentials anywhere online.
So yes, there's a risk but its not much different from going outside and leave behind hair or saliva unaccounted for. That's Putin level of paranoia IMHO(he is known to have men collecting his poo etc. when outside).
Maybe can be useful for insurance companies to match you and price you according to your DNA but they are not allowed to do that and they can only exist within legal structure.
Or just a part of it, which is the point: no, complete knowledge isn't required here.
Definitely not true, many services require KYC and others do it to prevent fraud.