i have seen quite a few other people with this problem with a huge other amount of data which they could not find where it was and never put i their device. Resetting the phone has worked with them.
Backup all your data which you want to keep and then press the bixby and power up button and press the power key and keep all 3 keys pressed till you boot into recovery mode, then navigate to factory reset with volume rockers and confirm it with power button. All data will be erased and you may be asked to re enter then pin if you had a lock method or to access with the same google account which there was before.
Important: again, back up all the data you want to keep because it will be erased and not recoverable.
If you have doubts do not hesitate to write it here.