Monopoly money is a figurative expression for "fake money", deriving from the board game "Monopoly", wherein players use fake bills as game pieces. I suppose it was ambiguous because I did not capitalize "Monopoly", my mistake there.
Okay, sorry, that was obvious in retrospect, I definitely feel kinda stupid now that I see it. In fact, I agree with your comment on almost all counts—I just see a lot of misuse of the term "monopoly" online, and I think I was led down a garden path by one of my sibling commenter's mention of Lina Kahn. No fault of yours, and I'm gonna delete my comment if I can :)