When I was very much doing 90% PHP work in my agency days (WordPress, Magento, Joomla...) I got some offerings for Magento but I mostly did front-end work in Magento and found it to be an easily breakable and over-engineered piece of work.
I didn't use Drupal at work but I was more interested in it. The Drupal job listings I have found were weird: They all required previous Drupal experience. I need a job to get Drupal experience but I cannot get it because I don't have it. I don't doubt that it would be a lot more versatile than WP though.
Not interested in founding a business with a partner or continuing freelance because it's too much uncertainty and risk for my taste. Just need a 9-5 with more stability. Permatemping gives me the worst of both worlds. You have to pay more on taxes, get no benefits, and you get paid less than you would if you were contracted from an external agency.
I'm not much of a social person, and since 2014 I started working remotely 100% of the time. I guess that physical isolation from co-workers was affecting my interview performance somehow?
Because the main issue is those 9-5 full-time jobs have super hard interviews, including the ones that don't ask you algorithmic questions. It's like they're on a different planet with how they evaluate me.
You want 9-5, and you don't want a boss, so permatemping seems to be one of your few choices. I was never that keen on having a boss; but I liked getting a reliable salary.
I have learned and adopted several programming systems (languages, if you like) over the years. One by one they were abandoned by their manufacturer, and I had to learn something new. I reckon it takes at least 6 months to get good at a new language.
By the time I was about 50, I noticed a trend for novel frameworks and languages to pop up with increasing frequency - more than one every 6 months. I found this increasingly teedious. By age about 60, I was no longer motivated to learn these new tricks, because they weren't going to be any use to me for more than a couple of years.
So: I concur with other commenters about taking up a job as a maintenance programmer on a codebase written in something unfashionable. PHP has always been unfashionable, and there's loads of PHP that isn't going anywhere and needs maintaining. You have PHP skills; consider Drupal. Plugging modules together to make Drupal websites is not challenging; but if you learn Drupal internals, you can be better than most Drupal "developers", and get jobs maintaining Drupal systems. Unfortunately, it takes time to get that level of Drupal competence.
Your "blue-collar" attitude is out-of-sync with modern software development. Nowadays developers are expected to be able to sell, teach, invent, write clearly, all the while avoiding antagonising people, as well as develop software.
Perhaps you could find a partner, with similar levels of ambition to your own, but with talents that complement yours, and set up shop together as a web-design agency. You need a production pipeline that enables you to build sites quickly and reliably. Your partner needs to have sales skills (it doesn't sound as if you do).
You don't want a boss; so I guess getting a job as a paid hack in a small web-development outfit is out of the question. But not all bosses are awful. And in a small firm, you might find that your experience makes a big difference to them, and that you are valued.
You sound a bit depressed. If that's true, I'm sorry. Things will improve. Good times and bad times are both temporary.