I feel a lot of employers are exceptionally bad at communicating their actual requirement. Ironically, one of the sure sighs that your job description is bullshit is having a line that says "excellent communication skills". Anything about "fast-paced environment" too.

Bringing it back to tech specifically, in my (anecdotal) experience people are rarely bothered by lack of knowledge of a specific framework assuming that the candidate has experience in something similar, or more generally if it is safe to believe that the candidate can get up to speed and contribute in a reasonable amount of time.

At this point we are of course just comparing anecdotes. I will also note, though, that there are a lot of very different subsectors within tech, and hiring practices vary widely between them. In accordance with the venue I am here mostly referring to startups (including late-stage startups).

I suppose the salaries of engineers are evidence enough that there is a talent shortage. Though, I've been perusing for a job and would not respond to maybe 85% of job postings because companies can't clearly articulate what they do and what the position they're offering is. I've been to plenty of interviews where they clearly haven't looked at my github, and then ask me odd, incredibly domain specific algorithm questions, and then turn me down as untalented. I've been to plenty of interviews where they think I'm talent, but in all their bragging about how talented their team is, I see signs of lazy engineers.

I think your judgement of how small the hiring problem is is way off. Coupled with companies' unwillingness to hire and train mid-level engineers to senior level (which really only takes a few months with an interested candidate) is the bigger problem.

Re job postings, most jobs are not filled through job postings. If you want to find a job at a company that knows how to hire, you will have much better luck if you find the opening through networking or a referral. I have literally never got an engineering job through any other channel. (Note that this does not serve as evidence toward your indictment of HR, most networking/referral hires still go through HR to at least some extent).