I'm going through that process as well, as I switch my projects away from coding and back to academic reading and research, which I have not done in 30 years.

What is working for me is to take it slow. To get actual books, not e-books, sit down with them in a cozy reading corner I set up, and read what I can. To go to libraries, browse the stacks, take a few books to a table, and skim through them. Basically, to avoid middle grounds and go all the way back to how I used to read before the web took off. It is not fixing my attention overnight, but I am improving over time.

It also helps to have a focus. Reading for its own sake doesn't give me the endurance I used to have, but deliberate reading to further some research goals helps me get more done.

Read fiction for fun. You don't need to optimise your reading time to maximise learning.

Read a paragraph or a sentence. If you got it, move on, if you didn't, re-read it but sound it out in your head. If you still didn't get it, re-read it aloud. If you still didn't get it, get some more sleep and try again another time.

One thing to keep in mind is that it takes practice. It won't be easy at first, even if your strategy is perfect. So don't be disheartened by bouncing off books or only being able to read ten minutes at a time to start with. Just keep trying, and over time it'll get easier.

Try this: never read without a pencil in your hand. Make it a point to not only orally or mentally restate but also rewrite by hand everything you read (on-screen and in real life) in your own words, and to make multiple drafts of each restatement until it is as succinct, orderly, and logical as possible.

This practice will probably help you:

* recognize and stop reading low-value material;

* read less on your phone;

* deeply understand what you're reading;

* identify errors in what you're reading;

* identify errors in your own understanding;

* improve your own writing (and possibly your handwriting!);

* recall what you've read and what it says and means; and

* build a record of your reading, reactions, and thinking.

And, of course, I think it should improve your ability to focus.

You can also make flashcards while you're at it (again, handwritten ones) and develop a spaced-repetition practice for the important information and skills.

--- Later Edit ---

You mention long-form text in particular. One of the most effective tactics to use while reading is to discern the writing's architecture/structure — at all levels, from the writing's genre, to its main components and their arrangement, to how each main part is composed, and so on. Doing so not only helps to understand and critique the author's ideas, but also becomes a fun game that keeps your attention directed.

And also keep in mind that > 99% of all writing is not only not great but also probably not worth reading in the first place. It's ok to use boredom as a guide: your mind may be indicating through boredom and distraction that what you're reading isn't worth the time and effort and attention it takes to do so. But if you have decided that you must read something, or that you want to read it and understand it, then I've found that there's no substitute for the handwriting technique. Check out the Mortimer Adler book How to Read a Book for further suggestions.

I faced a similar thing at one point. The thing that fixed it for me was going back to fiction. Started with a fantasy series. Did a little sci-fi. Did some easy classics (e.g. Dracula). Eventually that joy of reading, long focused reading, and effortless comprehension all came back. Just took practice.

Much like advice for writer's block being often "just write!". The same goes for reading. Start with something easy breezy and eventually it'll all start flowing again IMO.

Practice. I've had a couple periods where I went from reading constantly to not reading at all, and the only way to read more in one sitting is to read more. At the start you may only be able to do 15 minutes or so before you have to get back to the feed, and that's ok. Later that day you can do another 15 minutes, and tomorrow you can bump that to 30 minutes at a time. You can jump-start that by reading things that keep you glued to your seat rather than things that you need to read, like fiction instead of, say, an O'Reilly manual, but those books that are in the "want to have read" category instead of the "want to read" group are always going to be harder