Interesting to hear about the industry side. We have 20 chickens we keep as a hobby - a mix of hybrids and pedigrees. We can't tell the sex of some of these until they're weeks old, let alone at the egg stage.
Typical commercial sexing methodology is by holding the wings of the chicks out and looking a the feathers on the wing-tips. There are two sets of feathers there; if the feathers are of equal length, the chick is male. If one set of feathers extends further, the chick is female.
https://www.extension.org/sites/default/files/styles/large/p...