Theres a CGPGrey video that describes old techniques. It’s not quite up to date on some of its predictions, but it is how some machine learning works. Of course, it doesn’t discuss current proprietary techniques, because those are company secrets. Still, it’s as good a guess we’ll likely get, unless something radically different has been invented:

youtu.be/R9OHn5ZF4Uo

There is also a second video about more modern stuff, but it’s more a footnote:
youtu.be/wvWpdrfoEv0