We do not have a massive shortage of talent. I don't understand why people keep repeating this. If there were, interviews would be much easier. There wouldn't be this interviewing arms race.
Jobs that have actually had talent shortages do not operate this way. They hire candidates based on degree alone. Interviews are a formality. If they are really desperate they offer to pay the training of unqualified but interested people. The idea that they would reject multiple candidates with degrees and years of experience based on interview performance is absurd. No one is rejecting math teachers with years of experience because they failed to score 100% on a pop quiz about math, covering everything from set theory, to calculus and geometry. Sitting on the hiring side of the table at a big company, I saw us reject so many qualified candidates. The most absurd rejection was when someone with 8 years of experience at a FAANG was rejected for a Senior Frontend Role because they couldn't answer one of the interviewers pet questions about differences between MYSQL and Postgres. A situation like that would not happen if there was actually a talent shortage.
Also, the idea that there are all of these unfilled jobs strikes me as fairly suspect as well. I know someone who runs a startup and noticed that they had the same job posting on their site for a year. I asked them if they were having trouble finding someone and if I could help them by reaching out to people who might be interested. He admitted that they had no intention of hiring anyone, it was simply advertising. It makes them looks successful, like they were "growing". Having been at bigger companies where we rejected qualified candidate after qualified candidate, I suspect this practice is widespread. Better to project growth than to admit you are actually in a hiring freeze.
The last point I will make is that if there was a talent shortage, the bar would stay the same or decrease. From multiple discussions with people at FAANG, they have said the bar has increased markedly in the past 3 years. Again this is not something that would happen if there was actually a talent shortage, but would happen if there was a talent surplus.
There isn't a talent shortage because the candidates you interview don't talk about their projects up to your arbitrary bar.
Side note - I do NOT use whiteboard technique in my interviews. I ask the candidates questions about the stuff they mention in their resumes and go deep in the technical discussion based on their responses (or I told them to walk me through one of their recent projects be it a work project or their side project). Using that 'simple' technique, you can easily filter out so many pretenders (as I'd like to call them, who have splendid resumes but little to back things up when grilled the details about their resumes).
But asking about work projects specifically can be tricky, since you have to avoid any proprietary bits, to avoid any possible appearance of IP taint.
If they don't have open source projects to dig into, hypothetical plausible system problems (not leetcode exercises, nor puzzles) are an option.
You still have to watch out for people who know a lot of the right engineering things to say, and/or have done prep memorizing and drilling, rather than speaking from experience. (Example from one of the links in this thread, which had an example of a repetition flash card app, saying that UDP is connectionless. I don't know what good purpose would be served by having that info on a flash card for interview prep, other than to help someone who knows absolutely nothing about it to bluff their way through an interview that asks about it.)
From what I can tell, there's a sea of people who can barely do anything with some hand-holding, then each level of knowledge, competence and experience you want to go higher, you have to slice the pool by 100. By the time you get to level where people can competently drive non-trivial projects, there's a severe shortage.