I'm working on a very small project with MP4 video clips. The preview result is fine, but the rendered output file is all white. I've tried multiple output formats with the same result. I'm running 20.12.2 on Ubuntu 20.04. The audio on the output file is fine.

Any ideas what I might be doing wrong?

[Edit] - I tried outputting to a series of jpg files instead and the fade-in and fade-out to black at the start and end appear to be working but all the frames underneath are not white, they're sort of off-white beige colour. Weird.

have you tried also using an appimage?