Give this a try: go to settings > device care > storage > tap on the 3 dots in the top right corner > tap on storage settings, can you please provide me with a screenshot?
I would recommend clearing the cache for the Gallery, Samsung members app, files app. Go to settings > apps > tap on the 3 dots in the top right corner > tap on show system apps> tap on each app individually > tap on storage and clear the cache. Also I would recommend going to the Gallery app > tap the 3 dots in the top right corner > tap on trash and see if you have any pictures in the trash
I have done every completely as you mention which is clearing every single app caches and clean my trash bin in the gallery but the result doesn't have big changes which are only spacing up 2gb of my storage. Do you have a better solution to seek out the big file in my phone storage?
I would recommend backing up your device and performing a factory reset. Give this link a try for steps to back up your device and perform a factory reset: