If you haven't already tried this open device care, storage, Advanced. On the page that opens select Other apps, Files, etc for more detailed storage information.
I would try using Files to search for a Folder that contains the highest amount of storage usage. A good one to start with is the Android folder. Long press to select it and a menu will slide up at the bottom of the page. Select Details. This will show how much storage space the Android folder and all its subfolders are using. If it's using 40 or 50 gigabytes then open the folder and select the subfolder titled data. The data folder has a few dozen folders inside so look for a folder related to a gear app or something similar and check the details.
Galaxy S9 SM-G960U
Android 10 One UI 2.0
Security Patch Level
May 1st, 2020
Was this ever resolved?
I am having the same issue and I tried everything imaginable.
Device Care, Emptied Trash, Factory Reset etc. The "other" folder storage is filling up within hours, even though nothing new is being installed.