Discrepancy in image metadata: filename and DateTimeOriginal do not match

Hello all!

When I have a collection of images from several people, e.g. from a trip, I rename them based on their DateTimeOriginal metadata information, so that all images can be combined in a single folder and are ordered properly by name.

For the Fairphone 4 I noticed, that the name of the file provides a slightly different time than the DateTimeOriginal tag by zero to several seconds. I figure that the file name is when I press the shutter, whereas DateTimeOriginal contains the time when the image was processed and the saved, which might take a few seconds.
I did not encounter this with any other phone.

I think both timestamps should be the same and that this is a bug. How can I proceed?