The web version does require WIFI, but if you are running the Windows version, it does not. In any case, there is not much I can help with error code 500, as Ray_the_man mentioned the Itch.io servers might have gone down. Other than that, you can try these steps:
For web version:
- Make sure WIFI is on.
- Make sure you have a Chromium based browser.
- Open the game in a private tab/mode.
For Windows version:
- Try reinstalling the game. When prompted, choose the "Uninstall Tech Giants" option.
- Check "Delete the application data" (this will delete your saves).
- Install the game as usual.