Can't work with files on esp32

That's from the FAT filesystem again. It's the WebServer module you're using: https://github.com/espruino/EspruinoDocs/blob/master/modules/WebServer.js#L188-L189

Looks like when you init the webserver you need to be sure you specifically list your file:

    memory: {
        'web.html': { 
            'content': require("Storage").read('web.html'),
            'type': 'text/html'
        },

See https://www.espruino.com/WebServer#how-to-use-the-webserver-module