Ebooks, super easy to pick up and put down, and the E-Ink display solves the "can't focus" problem. I read theory on my phone though, a chapter at a time, I am working my way through a theory list that way. I find pockets of time, like traveling for work, lunch breaks, and other times I don't have my books or EReader with me, and I can't physically make myself sit and read theory for an extended time anyways like I can with good fiction.
Another huge advantage is the monetary value. Ebooks are free, especially public domain. My favorite site for high quality ebooks is Standard Ebooks. I can get whatever I want, read as much as I like, for the single purchase of an EReader and the time it takes to cultivate my Calibre library.
However, if I am alone, with a nice cup of coffee or an espresso in a nice morning, physical books are hard to beat. Same goes for some nice piano jazz, a glass of whiskey, and my favorite books in the evening. The latest to really get me that way was Piranesi. Turning the physical page, smelling the paper, it's relaxation at its finest.
I am thrilled to have rediscovered my childhood love for reading, it truly helps me in so many ways.
There have been a few times where I yoinked a book, read the whole thing, and then bought a copy fwiw. I try to support indies and such when I can, although I am very broke.
Oh I did that with Piranesi, yoinked it, loved it, bought it for my partner to read physically. Still, don't have the money I wish I did so I could support everyone, sadly