> I asked for an objective definition of what over-commenting would be.

I don't think what you're asking for is possible. It's an inherently subjective standard.

If an objective definition were possible, then it'd be possible to write a static analysis tool that reads both your code and the comments and flags "over-commenting on line 23, under-commenting on line 457". That could be done with sufficiently advanced AI, but at that point it would just be the subjective opinion of the tool's author being enforced.

over-commenting is explaining in pseudo-english what you've written in code. Prentend you are at the United Nations but you speak all the langauges, so you don't need a word-for-word translation. You don't understand to motivations of every speaker though, nor their cultural influences and a million other factors, so context is super important. In the briefings you get some of the information is not new; but if the vast majority of what you're told is obvious or discernable from what people say, you're looking at over commenting. It's not a yes-no thing but a balance of evidence, subjective opinion.