The “skill” line is what gamblers tell themselves to justify it. A much more useful demarcation is “does this game have any positive impact on the world” (entertainment value of the gambling itself doesn’t count). For example, insurance is not gambling even though it is itself a zero sum game, it enables societally beneficial risk taking. Options trading on real assets like stock aid in price discovery. Memecoins, sports betting, your local poker game and the way prediction markets actually function in practice are all gambling.