4.3 is probably why it works, any web exports from 4.2 require SharedArrayBuffer to be enabled in Itch.io. glad to know it's not needed for 4.3
the glitch happening with 4.2 projects, is when using the Game Jams Random Submission Feature, SharedArrayBuffer doesn't work, which makes any web build error upon loading. its easily fixed by opening the project without using the Random Submission Feature, but many people don't know that yet.