I've noticed similar errors. "Menu" not opening, missing some of the dialogue between missions. Right now, I'm unable to access level 2, even after completing the level for the access codes. It almost seems like some of the game elements aren't loaded into the program. I downloaded everything and followed the instructions to access "index.html", which opens the program in browser, but it's like part of the game wasn't downloaded. Not sure what the issue might be.
Have you fully unzipped the folder or are you playing from within the zip? I know on Windows it’s possible to open an html file without unzipping, which can lead to missing assets.
I'm on Mac. The download is automatically unzipped, and I've checked the other files to confirm there are no remaining compressed files. Is there a particular browser that works best?
I developed and tested on a Mac as well on both Safari and Chrome and I might've on Firefox too. Which browser are you on? I've noticed some weird stuff going on in other sites with Big Sur Safari so Chrome might be a better bet for now.