A perhaps better example: Nobody was able to verify Mochizuki's proof of the abc conjecture, because the first step was to spend a decade inventing an entirely

A perhaps better example: Nobody was able to verify Mochizuki's proof of the abc conjecture, because the first step was to spend a decade inventing an entirely new branch of mathematics. There are a lot of semi-coherent proofs for famous conjectures that appear from time to time on the arxiv, with absolutely unknown quality. P ?= NP is a popular topic.