Index File: An Error Occurred while trying to complete your request

Just had this myself, but having found another thread after seeing this one, a suggestion there was to check that Windows Defender hasn't suddenly decided to block the game's access to the files on your device. Seems to have worked for me 👍🏻

Edit: apologies, having just re-read your post I can see you did already try this yourself, my bad. Can't offer any other tips myself, since this did work for me so you're clearly facing a different issue, sorry! Hope someone is able to help you out soon! 🤞🏻