Just to shed some clarity on the purpose of this post after speaking with Andy. It was noted to me that the main purpose of the post (which admittedly seems to have gone off course after a point) was to suggest that the eventual replacement gallery app for GrapheneOS should make it easier to see an image's Exif metadata, and especially the "Date Taken" field.
In the meantime, please keep in mind that we understand that the gallery app that GrapheneOS comes with by default is not ideal (it's the AOSP Gallery app which has not been receiving too much love from the AOSP project). The plan is to replace this gallery app with a much better alternative, and a potential candidate for that replacement is already in the works.
Thank you for your feedback, Andy, as well as everybody else in the community!