What Is the Difference Between Date Taken and Date Modified?
Date Taken lives inside the photo and never changes. Date Modified belongs to the file and changes every time it is touched.
Date Taken is written inside the photo by the camera and stays there for life. Date Modified belongs to the file on your disk, and it changes whenever the file is copied, edited, or moved by some programs.
So Date Modified tells you about your computer, not about the photograph. A holiday snap from 2014 can easily show a Date Modified of this morning. Sorting by it scrambles a library.
Always sort by Date Taken, and fix it when it is blank. Takeout JSON Metadata Fixer writes the real date into both, so every app and every file manager agrees. It runs on your own computer and is free for your first 500 photos.