Please tell us some basic information before asking for help:
Model Name: ROG Phone 5
Firmware Version: RKQ1.201022.002.WW_Phone-18.0840.2106.86
Rooted or not: Not rooted
Frequency of Occurrence: Each time VLC app opens
APP Name & APP Version (If your issue relates to the app): VLC 3.3.4
This issue occurs each time I open the VLC app. Then when I click on 'GO TO MEDIALIBRARY PREFERENCES' and select Internal Memory, it shows all the videos. But once you temporarily leave and open it again i.e. switch apps or restart it, it again shows 'No media files found'.
I tried disabling Auto rescan in settings, and in that case the media files persist between switching apps and restarting VLC. However, in that case no new media files are shown. Only existing ones. And if you have deleted, they still show.
Attaching screenshot: