...and then I re-installed it and now launching directly just gives me a blank, white window, while going through a browser gives the same error.
Thanks for reporting it. Seems like this is an issue specific to the itch.io launcher(?). Also idk about directly launching index.html. As far as I know, it is supposed to run on a local server (running index.html by itself does not open a local server). Can you try running the game from itch.io itself? The browser-playable version? It should work in that case. Thanks for your patience.