How hard it is to actually get to level 20?

I've got into dnd thanks to Baldur's Gate 3 in 2024 and I've been obssesed with it ever since, bought the books and everything. Now, after reading the player handbook in 3 days thanks to the powers of autism, I saw that level 20 is the pinacle yes? All powerful and all, you can basically do everything your class offers but... how hard it is to actually get there? I've heard of players that play the game for years and never got to level 20 with none of the characterd they made.