I do see some listed counterexamples to the "law", and also a note about occasional upsets where the parties get completely rearranged.

If both major parties suck, how do I ask for an upset? Is it by fuming quietly and voting for the lesser of the two evils, or by saying "no, fuck you both"? Or does the fact that any upset probably won't happen this election mean that it's part of "the long run" where per Keynes we're all dead, and so it doesn't actually matter?

Do the major parties just ignore any non-major-party vote, or do they analyze it to tweak their platforms for next time? (And, is this consistent over time and space? I'm hearing that it seems to be the case in the US now, but in the same breath I'm hearing that that's a recent localized disaster.)

The Wikipedia page is a tremendously short summary, and yes, doesn't go into depth about the implications of duverger's law.

I strongly suggest digging into the literature around it, which does bear out the thesis I states above.

If both parties suck equally and no party is more closely aligned to your preferences than another, I suggest you enter politics yourself. It's just made up of people not too different from yourself.

I've actually thought about that a bit, and don't think I'd enjoy it enough to consistently put in the time needed to ever really get good at it.