What Is Date Taken?
Date Taken is the moment the camera pressed the shutter, stored inside the photo. It is not the same as the file date.
Date Taken is the moment the shutter fired. The camera writes it inside the image file, in a block of information called EXIF. It travels with the photo, so every app on every device shows the same answer.
The file date is different. That is when the file was written to the disk you are looking at. Copy a photo and the file date becomes today, while Date Taken stays put. That is why one is trustworthy and the other is not.
When Date Taken is empty, apps fall back on the file date and your library falls out of order. Takeout JSON Metadata Fixer fills it in from your Takeout .json files or from the photo itself. It runs on your own computer and is free for your first 500 photos.