It doesn't list any scenarios when I go to create a new game.
Note: when it is loading and asks "Select your RCT2 data path Pick your RCT2 Data Directory" it actually wants you to pick the parent directory containing Data/
So what's the use case for running it in your browser other than just for the sake of it? Would it be possible to host the game files on a server and then load the game in a browser on another system?
Emscripten's user agent (browser) Javascript is quite cryptic and was rather difficult to adapt Emscripten-compiled WASM to custom web apps. (Had to look at Emscripten example web app.) Congrats.