It is 100% required for employment-based green card from a H1B. Anyone that has gone through this process knows this as their own job had to be posted to several job posting sites and each and ever candidate had to be reviewed and discounted in some ways (my company added crap to the posting such that it was simply impossible for someone to be as qualified for the job as me unless they sat next to me and did what I did for 5+ years…)

Nope, it's not 100% required, there are exceptions for certain job categories like nursing and there's also the extraordinary ability exception.

(Not trying to be pedantic but US immigration law is full of random loopholes and people who qualify for them, or might be able to qualify with a bit of work, often aren't aware.)

I should have been more clear - I am talking about IT/Dev/… jobs, not other professions.

Not sure if it’s still the case but extraordinary ability green cards used to be surprisingly easy to get for software engineers! Get your name on a patent (not as hard as you think, companies love adding to their IP portfolio), get accepted to do a couple of conference talks, and you’re most of the way there. Or so I was told a few years ago by someone trying this route.