I was running BigSur on a mid 2015 iMac, but realized that I needed to downgrade to Catalina to run a specific program. I bought a WD HDD, used time machine to back up my computer, and then successfully erased my iMac and installed Catalina.
However, now I can't see the contents of my WD hard...
I'm running an early 2015 MacBook Air with Sierra 10.12.6
I have recently started editing video. I have iMovie 9.0.9 installed.
There appears to be an incompatibility between these, such that my shared/saved videos are colour washed-out.
I'm caught in a situation where my computer cannot run...