You dont need to install the codec to edit HEVC clips.
BTW codecs are not needed to do certain effects.
Make sure you have access to the document folder.
On a side note, the hevc codec is not available in trial version.
and Please tell us your system specs: OS version, Premiere version, amount of RAM, Hardware specs including graphics card. If I remember correctly HEVC is not compatible with earlier versions of premiere... And even when it's compatible, HEVC is a bear of a codec and can slow many systems down to a crawl...
I'm using windows and currently at this moment of time I check what version it is on. All I know is I have the latest Windows & Premier Pro updates. I have 48 GB of ram, rtx 3070, and an i7 9700k.
All I know is something is downloading properly.
All I know currently is that I am missing 2 files from the codec folder and they wont reinstall themselves. I have sent an email to support but havent heard back yet.
The issue was that I didn't have a certain permission to access that folder. When I switched to another administrator on the computer and ran Premier it installed fine.