OK, but this happens all the time now, which is pretty annoying. I have the same problems when opening downloaded mp4 videos using QuickTime Player after the update to 12.6.4 and 12.6.5. I download videos using Firefox with "Easy YouTube Video Downloader Express" extension, for later offline viewing and archiving. That worked great so far and it still works on my older Intel iMac (macOS 13.6).
Immediately after downloading the video (usually 720p) it is possible to open and play it back. Now on my MacBook Air M1 with macOS 12.6.5 it also needs two reboots of the machine and the video will open and play back on QuickTime player. What is going on there?
Using VLC Player instead of QT Player, the video plays back immediately after download.(!) This very strange. Does some Apple technician have any good advice what to do? Two reboots aren't a really acceptable solution to the problem, IMHO.
One more thing: After the first update to macOS 12.6.4 I noticed some strange changes to the file permissions and ownership in my home directory, that prevented opening some of my text-, jpg, or psd files. After further investigation I was able to find that out and to fix the problem, but that shouldn't have happened after a minor macOS update.