Columbine was absolutely not that. Klebold and Harris were nazis and it’s no coincidence they did it on 4/20. They tried planning attacks in other places but couldn’t get the logistics of it down so they shot up the school instead.
I read a 400 page book on it by a fairly neutral professor/academic, from what I remember, this was in 2016 or so, it was a lot less clear than that. And mostly meant the idea that they were bullied and the "trench coach mafia" that part of it.
Nazism adds context but not really motive to almost indiscriminate murder of classmates.