I have a QuickTime video of a digital clock for sports videos, just animated white numbers on a transparent background. It works fine in Vegas v18, but when I imported it into Premiere for the first time today, I just got shown a black box! Not only did I lose my transparency, I'm not even seeing my white digits!
I tried re-wrapping the MOV in AME, but even Media Encoder was only displaying solid black when I scrolled through the different codec variations.
It displays fine in my old Vegas 18 (which I still use for advanced audio purposes), so I just exported an MP4 of the clock with a green background and used Ultra Key to regain my transparency.
When Googling about Premiere support for MOV files, I saw a remark criticizing how it doesn't support 'QuickTime 7' anymore, and this guy couldn't use his legacy footage filmed in that format. I'm a relative newbie to video and all these Codecs, but I'm guessing the clock is a QT7 file, which is why it displays in old Vegas software but not Premiere 2022. Anyway, I fixed it with a 'green screen'.