It seems like itch.io does not use cross-origin isolation, which means WASM threads are not supported, which can be used to help performances, for example decompressing textures in a thread instead of the main loop.
Are you reporting this for the app specifically, or for playing games in your regular browser?
You will minimally need to enable this option to ensure that you have access to the elevated APIs: https://itch.io/t/2025776/experimental-sharedarraybuffer-support