cannot update because error code 4000

I just updated my iPhone 11 Pro Max to iOS 14.7. I have had the problem you described for a while now but this method worked for me:

First, go to Face ID & Passcode and toggle "USB Accesories" ON. (I don't know if this step is needed, I just did it just in case. You can toggle it back on after.

Then, download the .ipsw update file.

Then, in iTunes, hold down the shift key and then click the "Update" button

Go to C:\Users\YOUR PROFILE NAME\AppData\Roaming\Apple Computer\iTunes\iPhone Software Updates

Select the ".ipsw" file you downloaded.

My iPhone update then completed successfully.

This way, you don't have to turn the Passcode off, which will delete any saved payment cards in Apple Wallet which you will have to reenter.

Error 4000 is a Windows 10 and iTunes error. Until Apple updates iTunes, you will continue to receive the error if you attempt to update or restore your device in iTunes. A workaround for now is to temporarily disable the passcode on your device, update, then put the passcode back on. The con to this is that it will remove all of your credit cards in Apple Wallet. Another option is to go to Settings>General>Software Update and update from there.