The book was too hard, and it is the standard mistake. Nothing is wrong with you and reading does work at your level, you picked the wrong first text.
The rule that matters: you should understand most of it without looking anything up. Roughly one unknown word every few lines is the range where reading is productive, because you can infer from context and keep momentum. Thirty lookups on a page is not reading, it is decoding, and no amount of it builds fluency.
So the path in:
Graded readers. Books written for learners at defined levels. Unglamorous, and they are how a lot of people actually make this jump. Start below where you think you are.
Children's and young adult books in the language, which are the usual next step. Note that children's books are not always easy: they often use unusual vocabulary and playful language - so young adult is frequently the better bridge.
Something you have already read in your own language. Enormously helpful, because you know the plot and can carry meaning across the gaps.
Non-fiction on a subject you know well. You already have the concepts and half the vocabulary.
Then a normal novel, later, and it will feel unremarkable when you get there.