Doing things for the fun of it, for curiosity's sake, for the thrill of solving a fun problem - that's very much alive, don't worry!
Maybe just have a cool advent calendar thingy like a digital tree that gains an ornament for each day you complete. Each ornament can be themed for each puzzle.
Of course I hope it goes without saying that the creator(s) can do it however they want and we’re nothing but richer for it existing.
It becomes a race when you start seeing it as a race :) One can just... ignore the leaderboard
Many people do - well, did - AoC while ignoring the leaderboard.
Even before LLMs I knew it was filled with with results faster then you can blink.
So some of us, from gut feeling the vast majority, it was always just for fun. Usually I spent at least until March to finish as much as I did in every year.
> Having a leaderboard also leaks into the puzzle design.
Instead, getting gold stars for solving the puzzles is incentive enough, and can be done as a relaxing thing in the morning.
No matter what you do, as the puzzles get harder, you won't solve them in a day (or even a lifetime) if you don't come up with good algorithms/methods/heuristics.