I'm familiar with this situation myself, so I can empathize. However, I can also see it from the other / hiring side of the equation.

I hope you will excuse me for delivering some tough love, as a lot of your narrative around this is not as objective as it could be.

* Nobody cares about your "unique experience", "unique set of circumstances", "this confluence of unfortunate events", "heavily scripted and impersonal to a fault" etc... "You are not special. You're not a beautiful and unique snowflake. You're the same decaying organic matter as everything else. We're all part of the same compost heap." The only thing anyone cares about is demonstrable ability to develop software.

* Nobody cares about "20+ years of software development". If they did, they'd put it in their job descriptions / requirements. Rather, they care about 3, 5, maybe 7 years of experience. Anything that comes before that is irrelevant. Only in highly specialized fields, or senior management, is extensive experience an asset.

* "what have you done lately?" - well, what _have_ you done lately? Do you have a good answer to this question, mentioning only things that you have done, and not any mentions of uniqueness? The reality is that people hiring for software developers see having developed software in the very recent past as indicative of someone who can be productive in the very near future. Explanations of unique circumstances and software development experience several years ago won't cut it.

* "Does someone with my experience really have to grind leetcode and memorize algorithms to prove his capability?". Well, yes. Frankly, given your level of experience, brushing up and kicking ass on leetcode should be a walk in the part, and nothing to get indignant about. If entry level / fresh grad folks are expected to be able to do this, you should be able to do it too (and more). "20+ years of software development" doesn't get you a free pass on this, you should be able to do it all day, every day, in your sleep at this point.

* "Is it realistic for me to expect to be able to work on a software team again after having transitioned away from software development?" - only if you can demonstrate your ability to develop software here and now, and in the near future, as distinct from years in the past.

* "I'd be interested in management" - do you have management experience, which is articulated in your resume, profile, applications, etc? That means performance management, hiring, firing, project management, powerpoint, stakeholders, etc., etc... it's not a given after "20+ years of software development", it's a distinct skillset that you may or may not have developed.

* "I know I'm fully capable but I've found it difficult to prove that to ornery employers employing what I see as broken hiring practices" - nobody cares about your opinions on hiring practices. When you start your own company, you'll be able to institute your own, superior hiring practices. Until then, it would be in your best interests to focus on the hiring practices as they exist, rather than how you wish they were. Proving your capability, given the hiring practices that exist, is what it's all about.

* "I've been involved myself in hiring for several years and I always made an effort to take an empathetic approach with people I interviewed. Sadly, I seem to be one of few who take that approach." Nobody cares about empathetic approaches. They only care about demonstrated ability to develop software.