I'm wondering if we'll reach a point where it is impossible or nearly impossible, and what value of 'understand' we assign to it. For example deeply understanding x64 processor architecture. Does any one person understand it all, very unlikely at this point. The investment the average person would have to perform to accomplish even part of that would lead most of them to seek other more fruitful endeavors. Biology would be a good example of this. Nothing about biology is magical, and yet even simple systems contain such an information density that they are at the impossible to fully understand point, and that's before we start layering them into systems that have emergent behavior.
Scale.ai (no affiliation, not a customer) has a product called Spellbook