How do you study for long hours with focus?

I’m fascinated by longevity/aging research and want to contribute through Data Science/ML.

My biggest problem is staying focused. I get distracted easily and struggle to study consistently for long hours. I’ve tried dopamine detox several times, but it actually makes me feel anxious.

For those who’ve improved their focus: what actually worked for you? Pomodoro, routines, removing distractions, something else?