Some anecdotes, specific ways it can be unclear how many job openings exist:

I applied for some jobs, two of them liked me and I reached the point where they were competing with each other for me, and I was in salary negotiations. One of them, suddenly, decided to stop trading. I still don't know why.

Another time, I started working(!) and getting paid, but after 6 months the person who everyone (including themselves) was expecting to leave and for me to replace had still not found a new job (presumably due to all the ghost jobs), and there wasn't enough money for both me and them. Last in, first out, bye to me.

One place hired an PM about two weeks before the investors decided to shutter the entire company. (For actual ghost jobs: in my own job hunt after that, I found listings on job boards for that company, that were clearly from several years before I'd joined given the advertised wage range; as the company had told everyone to stop coming in for their notice period, there wasn't even anyone left to ask for those to be deleted).

Back when my dad was around, one of his anecdotes about interviewing candidates was asking the candidate "Why did you leave your last job?" and getting a reply along the lines of "After 6 months, management found out that our entire floor had been hired to do the same thing as the floor next to us. One of the floors had to go."