Answer: Can you check the "Recently Deleted" folder? You may find this in the "My Files" app. If this does not work, and you can confirm you have no backups whatsoever, then your photos are as good as gone. This has happened to Android devices in the past (or Samsung devices mostly) where all their media would just disappear. As far as I know, all Samsung themselves say is to restart your phone to try your luck. An app crashing or some form of corrupt media may have caused your photos to go missing. There may, however, still be a small chance that the photos are there, somewhere on your phone, you just can't find them. I advise checking the storage in "Device Care" and see if the Gallery app is using much storage. If it is, I would connect it to a PC and look through the files again.
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