I think this is about where I realized your anxiety has more to do with your financial situation than your technology situation. Your worries are about the way you spend money, how much you spend, what you spend it on, and how corps try to part you from your money. Like another commenter said, all the free and open technology in the world isn't going to magically balance your checkbook... though of course, it will help!
Yeah installing Ubuntu is great, learning to code is great, these are valuable endeavors if for no other reason than just to learn and try new things, but you don't need to learn programming to "convert your chromebook to Ubuntu."
I have no idea what to do about Amazon or Amazon Prime. ... things that, in a small town with a particular disability keeping me from driving, I can only get on Amazon.
If using Amazon is unavoidable, then it is what it is. There's no shame in using them to get what you need. If you're concerned about, say, your habit of impulse buying (not an accusation, just an example), you could try setting up a secured credit card with a spending limit so you can only use it for exactly what you need.
death consciousness of mindlessly scrolling through Facebook
Block Facebook in your router settings (or get a Raspberry Pi, install Pihole, and set up a block rule there). If you need Facebook to communicate with friends and family, could you rely solely on Messenger? That way you don't need to see anything on Facebook other than your DM's.
If your mental health is dire enough that all that's not enough, you probably need a therapist. You can even get it through some tele-health programs (YMMV). Hope this helps!