what browser/version are you using? What does the console say when you open it up?
I just pushed a patch that might fix the issue.
I was able to reproduce the bug on my very old chromebook (Chrome version 93 or so.) It turns out that the game was working normally except that the canvas was being set to be zero by zero pixels big for some reason. I changed the flags I provided when initializing the SDL window, and that fixes the problem. I'll investigate further and file an issue in the Emscripten repository.