An unknown error occurred when update my iPhone (4000)

Here’s a user tip on this long-standing issue with iTunes for Windows→If you see Error 4000 updating your iPhon… - Apple Community

Hello Fa6iima,

We see that you're having trouble updating your iPhone. We'd be happy to point you in the right direction!

The article listed above has some great steps that can help resolve issues like this. If the steps in that article don't seem to have done the trick, you'll want to reach out to Apple Support to look in to some options.

You can reach out to them here: Get Support

Take care!