Can a Windows computer back up absolutely everything Android
Don't confuse being able to
store files on a particular OS's hard drive with being able to
use files on that OS.
Because I'm an avowed window$ hater, and Linux ONLY person, I don't want to steer you wrong. But I believe that any OS, even window$, is capable of having files stored on its drives without damaging them.
Unless, of course, a human comes along and does an ill-advised move, like opening a video file in a text editor, making changes, and then saving it. Poof! That video is now toast.
Barring that type of interference, any file--intended for any operating system--should be fine on another OS's drives.
And that's all we're dealing with: files. It doesn't matter if they're images, music, videos, text, etc., you should be able to copy them to your computer and they'll be fine. Just don't expect, for example, an Android game to be usable on a window$ PC.