VLC on iPhone\iOS shows blank screen but with audio on TV (via AirPlay on Apple TV) since upgraded to iOS13

[DnD]

I think they mean Screen Mirroring (accessible from iOS control panel by tapping the icon which looks like two rectangles overlapping)

I literally created this account only to thank you for your reply!
Turning screen mirroring on first and then playing the video in VLC makes the video show up on the TV in full-screen.