Nicaea didn’t definitively settle the Biblical Canon, or even take any steps in that direction. The fringes of the canon continued to be discussed with some intensity through the early fifth century, and only Trent definitively settles the issue. A number of late 4th and early 5th century local gatherings made practical local decisions on what would be used liturgically, which did point the way to the ultimate solution, but it was over a millennium in being ratified. (Last month I was reading John Damascene, writing in the 8th century, who excluded but quoted the deutero canon but included Clement).
I have long been impressed that only a few years after Christian persecutions, the Roman Emperor, Constantine, could call a council to begin to address defining the Cannons of the Church even as you point out that the discussion of the issues continued over a millennium.
Please allow me to disagree somewhat regarding the Council of Trent, as I am a Protestant and the outcome of that body was the permanent rejection of any Protestant faiths as against the doctrine of the Roman Catholic Church. I suppose to you, I am in the first category of crazies.