Older project not playing or displaying any files.

[BrownFish]

I opened a project created before I moved to Big Sur. That project is now entirely unresponsive. Timeline will not play. Timeline monitor does not show anything when I scrub (black screen only). Revealing source clip does not show the clip’s video image either. It “sees” the media. But it will not playback in any way.

The latest version (14.8) behaves the same way.

Fortunately the BETA version does indeed playback(!). So that means I can’t trust the latests authorized versions at all. I’m going to run in Beta until I’m certain that Adobe has fixed the issue. 

[BrownFish · Accepted solution]

It appears it was related to old Blackmagic drivers on the Mac that were not compatible with Big Sur. That explains a lot of issues.