I've been through so many puzzle dungeons that I immediately just exit a process if it involves another technical interview. I've done technical interviews with FAANG and the like and those processes actually tend to be much nicer at more mature companies because they're actually well designed problems with people who actually understand their significance. You at least get to ask questions and not just get told to jump through the hoop like a dolphin. For the rest, you end up with interviewers who google some esoteric Python problem they think is particularly clever.

I'll stop here to state that I think any adherence to being overtly clever is my first and only red flag.

It's so pathetically obvious because the number of times I've done the exact same problem for multiple companies because it happens to be the 2nd or 3rd search result.

I once had someone disqualify my answer for using a DFA because it wasn't "real code".

To be honest, I think the technical interview actually IS important, and I've had numerous experiences enjoying it if only to showcase a lot of the more necessarily toxic behaviors of a company up front. Let's be honest with ourselves, is any employer going to necessarily have the best practices with respecting your time, money and effort? It's best to lay out those cards up front. Literally every red flag will demonstrate itself through the interviewer in most scenarios. Like any test, you get out of it what you give.

For example:

How many times do I feel this?

"We take an extra time-slot / day / email chain in what is already a hypercompetitive market just to suss you out. We wait until the last stage of the interview process to do this because we still don't totally trust you or understand anything you've done. We waste a lot of time creating elaborate puzzles that don't really matter. We're not going to pay you because our finances are already horribly mismanaged that it's complicated to contract you out for the day and also we feel like you should be gladly externalizing your labor costs for our shiny position if you really love us. Drink the kool-aid."

Sometimes the technical interview surprises me. I always use it as a motivating example of myself as a candidates to work through a problem, show grit and also demonstrate when to ask for help. Ego and pride on both sides of the equation come into play and that's always a worthwhile exercise before engaging it any longterm commitment. A good test accommodates and informs through failure. I learned this from administering the Putnam. Never got a decent score on it, but it was a worthwhile experience to fail. Interview tests are on the other hand, are not designed to teach anything except that you are unworthy.

My best roles have never asked for it. The company knew what they were looking for, were willing to trust me, were able to move along the interview process without losing me to a competitor and everyone was happy and they always pay competitively. Usually if there's a technical interview involved at all, they have no idea what I can actually do. If they're willing to waste time, effort and money on extra steps and are taking "necessary precautions" to subject you to what are essentially just litmus tests, then I'm sorry, that speaks to me a sense of your culture of mediocrity and dogmatic orthodoxy towards process.

Goodhart's law. When a measure becomes a target, it stops being a good measure.
When I was in school, we had other students take a year off to study for the Google interview. These were all affluent white men. At the same time, I had recruiters complaining to me that there were no decent black/brown candidates in the pipeline. I remember hearing the same thing except as a child. Uhhh, there's been plenty of time to invest into the local community. Recruiters would do well do understand to the history of the SAT as systemic racism, or literacy tests as systemic racism, or like any actual statistics as systemic racism. Everything that reduces candidates to numbers and quizzes feels rife for abuse. Who has the privilege to study an extra game on top of performing in a society that is already stacked against them? That's not a question.

To wit, there's the issue with a large number of candidates with junk resumes. There's the outstanding issue of "authenticity" in professional acumen. There's the whole problem with the industries underlying predatory behavior with regards to labor externalization and laundering numerical metrics, be it the rate of inclusion and diversity or the amount of hours actually demanded by management. What is so fundamentally wrong with the technical interview is that it's just the cherry on top for what is already a miserable process. I'd so much rather just do free work for a potential client and just give it to them so it actually means something and is useful than waste any more time solving pointless puzzles, and this is from someone who specifically enjoyed studying hard pointless puzzles in school.

No, you can't just show side projects. You should not be showing your work portfolio to anyone who isn't paying you. If they were interested in open source, they'd already be paying you.

The technical interview is dead. Long live the technical interview.