That would be (I think): capii moltissimo.
You need to include the plural noun "cose." They aren't looking for a similar phrase that means something like it, but a translation of the Italian.
I understood so many things also not accepted 29 July 2017
There is a difference between tanto and molto, one which is expressed by "so many".
Since this is passo remoto, does this mean I no longer understand so many? So true.
It certainly can have that connotation, given the context. It can also mean you still understand what you understood:
"I understood so much back then. As I've gotten older, I no longer understand things as well."
"I understood so much back then, but I didn't have the wisdom to apply that knowledge in any meaningful way. I've increased my knowledge very little since then, but years of experience have made that knowledge so much more useful."
What tenses would you use to write this news report: "The crowd went crazy and ran over each other after the explosion went off." I'd use two different tenses.