For future reference, when doing a WebGL build in Unity, disabling Compression under Player Settings in your preferences gets it to work. Itch really doesn't like something about Brotli compression, I guess.
I had a similar "ball and chain" platformer type idea, so its interesting seeing someone else's take on something I didn't end up doing! I feel like if you wanted to go down the route of a skill based platformer, a way to aim where you're throwing the weight would really benefit this game. Theres also a lot of potential in this being a puzzle game instead of something where precision is needed. Entertaining game though!