I was like this too and was so frustrated because I used to love reading. I asked my therapist and she said to stop using my phone (and reddit lol) so much. My brain is addicted to the quick dopamine hit you get from funny cat gifs etc. So I started limiting my screen time and that absolutely helped.

I also started picking books that were shorter, less challenging and more immediately rewarding (gossipy Hollywood bios, short adventure novels etc).

Everyone is different but that's what worked for me!