This problem seems to accompany upgrade to Premiere 2023. When exporting 4K HEVC at any bitrate I get choppy, lagging response when trying to scrub through the video in Quicktime 10.5. My M1 Pro Studio w/64GB RAM and ample storage does not seem to be an issue. Exports of the same timeline from previous versions of Premiere using identical settings do not cause the issue. Scrubbing is fluid and clips display fully in a file exported from Premiere 2021. I also note that, following upgrade from Pr 2021 to 2023, clips do not render in the timeline at the bottom of the QT player window (see attached screen grab). The timeline is black. Any help would be appreciated. As a follow on, I tried playback in VLC. Same results. This seems to be a Premiere issue.