No one says it’s common. But it’s not 1 per million, it’s 1.7%. In Canada, that means there are around 680,000 intersex people.
https://pubmed.ncbi.nlm.nih.gov/12476264/
It proves that 600,000+ people in Canada do not fall under the normal two sexes.
You seem confused…
Do you understand what I typed above about the exceptions to biological sex? It means that biological sex isn’t binary. You even said there are rare exceptions.