Trying to import HEVC-encoded MP4s

It's worth noting that trial versions of Premiere don't support HEVC - or at least historically they haven't. And I guess since you said you have a 2020 version I should provide a little more context. There are definitely legit ways of having older Premiere versions than what is available on the CC app - I still have 2019 on my older mac laptop, myself - but if you had an unlicensed version of Premiere then it could be based on the trial version. 

First thing, is don't drag/drop media from Finder/Explorer into Premiere's Project panel. That can work mostly sort of, but doesn't always get the full meta from a file properly loaded into Premiere's databases.

Use the Import option from the Project panel, or the Import or Ingest options from the MediaBrowser.

That said ... some drones & phones do use intriguing options very rarely 'seen' in H.264/HEVC in-cam created files. Those can be an issue at times.

Neil