Governance seems more invested in making ideological changes (dropping Webpacker, TypeScript, breaking changes between versions that add busywork but no value) than building the community and expanding reach. DHH continues to push poor technical decisions and alienate contributors by taking weird political stands.
As someone who’s taken multiple projects to production in Rails and generally loves Ruby, these days I prefer to start new projects in full-stack TypeScript. RedwoodJS has been quite good.
How can I learn about these topics? Junior self-taught dev, I read these things and kind of see what they're about, but I wouldn't know where to even start with this...
You can practice the mindset by writing a toy solution for the problem, then listing the reasons why you consider your solution just a toy. This develops a fundamental skill of engineering, which isn't understanding whether a system will fail (it will always eventually fail, even if the first reason is that the sun explodes), but rather when and how it will fail. You can make a whole career out of pulling on that thread.
(I worked at Google with Bob in the mid-2000s. I might have interacted with him once or twice on the internal Java and Guice mailing lists, but never met him in person. He was supremely helpful and knowledgeable, and I admired him from a distance.)
Designing Data Intensive Applications (DDIA)[1] is a great introductory book for such things. It covers a broad number of system design topics, and you can then go into detail for stuff that interests you.
Other than that, several companies (such as Uber) operating on a large scale maintain engineering blogs.
For someone who knows nothing about self-hosting, where should I start? I'm a self-taught junior dev but haven't had a chance to dabble with any aspect of deployment yet... willing to learn though.
Setting up your own DNS like pihole and a personal vpn to enable you into your home network when outside is usually a good starting point. Or even simpler and potentially useful setup your own gitea instance, it's easy just use the sqlite backend.
Set up a basic web server, then try something like WordPress/Drupal (with some database backing it)... then maybe SMTP/IMAP with spam/av filtering and a web frontend (roundcube/squirrelmail)... that will probably keep you busy for a few months :)