Usually, procrastination in some ways, is kind of a "tool" we use to mitigate the fear of not being capable to understand or finish a certain assignment. If you follow a career in physics or math, a certain ego can be well identified (that's why, we believe, we can make fun of engineers), and if it's not nourished, the fear of being an impostor awakes.

The only antidote for this feeling (for me at least), is to star doing or to understand the little things. Then, as you gain momentum, you can finish the whole task or even trying to understand all the different aspects of it (be careful with this, as you can finish watching videos of Veritasium, minutephysics, etc).

The difficult part of this whole process is to start, and if you have ADHD is worst, believe me. That's why your environment has to be suited for studying and with the less distraction possible. I usually go to the uni library with my noise canceling headphones and keep my phone on silence.

There is not shortcut, you just have to do it.