If Apple would make it so that websites can’t request to enable notifications, but only via manual user action, I’d still prefer that to developing an entire app to fit that goal.

You’re very much making this out to be more difficult than it actually is. If you’re a webdev throw a web browser frame in, or use react native, or just spend the few hours it takes to learn how to setup and app and push notifications and add a bullet point to your resume.

Not sure what I need a resume for. I'll probably never work for an employer and I think I'm a better farmer than a webdev.

I know how to design and build things with my hands. I also know how to design logos, websites and other things. I can code and enjoy building and maintaining the network of websites I built in the past 15 years.

But I feel I'm spreading myself too thin when I'm also learning to code in React or Dart (Flutter) for a single one-off project. I fear I won't be able to put in the hours required to become adequately proficient in another field that's constantly changing.

No you are not spreading yourself too thin. Each new language or framework you learn will teach you something you’ll use for the rest of your time programming. You may not remember everything you learn exactly, but it will help you carry conversations or know where to start should you be tasked to need those skills in the future. Also Google is your friend, you’re never going to know some language or framework so completely that you can verbatim spit out it’s docs and signatures without some reference.

The rest of what you said sounds pretty on par with the rest of the self taught programmers I’ve met (me being one of them).