Just yesterday, I noticed that my phone couldn't open any new photos. It'd just say "unsupported file." I tried resetting the camera setting, on and off, but nothing help.
Sounds like something may have gotten corrupted. Have you opened your DCIM folder in file manager to make sure the picture file extensions have not changed? Check to make sure that high efficiency pictures is not turned on (it may interfere with the gallery or other apps opening the photos). Here are some things you can try, checking in between if the issue has resolved, as there is no need to go through them all if any one thing helped.
1. Try going to device care and optimizing your phone
2. long press on the camera app icon and when the menu comes up, click on the the circled "i" to bring up the app settings. Scroll down to storage and clear the cache and data.
3. Reboot your phone into recovery mode by pressing and holding the volume up and power buttons until it restarts and you see the Samsung logo. As soon as you see the logo let go of the buttons. You should then be in the recovery screen. Use your volume up and down buttons to scroll to "clear cache partition". Select by pushing the power button once. You will see a warning and you need to select yes to confirm by pushing the power key. Once you do that, you will get a message say the cache has been cleared, and you are presented the option to restart, select that, and push the power key. The phone will boot normally and you can check if that helps.
