The ability to focus is like a muscle.
It atrophies when not used.
It needs to be exercised regularly to build.
And it gets better with more exercise.

I used to be good at reading when I was younger. Reading long form articles and books happened with ease, even with non-fiction like textbooks.

My ability waned when I started working. With working came reading short form emails, and no books. I remember when I wanted to read Pirsig's Zen and the Art of Motorcycle Maintenance. It was 2008 and I was in my own apartment. I had full control on distractions.

I remember it being so difficult to focus that my mind would wander at half a page of the paperback. I wold drift away on several tangents often. The dry metaphysical topic did not help either.

Switching on music started to help. I would play some electronic music that prevented my mind from going on as many tangents while reading. It took a few months for my focus to start getting better. The music started to feel like a distraction. Just like training wheels become a bother when we learn to balance a bicycle.

That thing you used to be able to do but can't do any more?
Well, find your training wheels.
Give it a go.