Hydrogen page alternates

Hi found issues mentioning it and also part of the source, but I cannot understand where the alternates comes from when you use hydrogen.

It is possibile to have a product published only to a subset of markets and I cannot find a way to retrieve given I am in a market X with language Y the sibiling urls to handle the hreflang tags.

alternates seems to be handled also in a common utility, but I cannot find where the data comes from given that I did not found any property on the SEO field.

Even in the example store of hydrogen I cannot find that.

Thank you