Samsung "My Files" Downloads folder corrupted on non-rooted phone
There is an app named Media storage in Android OS that stores the database of files and folders in the storage of your device. Looks like there is some problem with this app, so you need to clear it's data and cache.

To do that, go to System settings->Apps, click on the menu button (3 dots) then click on Show system. Then, in the apps list, you can find an app named Media storage. Click on it and clear it's data and cache. See this screenshot :