Error Exporting Video from Photos App on Mac

Hello,

My basic problem

In the past few months I've run into a problem where my iMac can't export video from the Apple Photos app. When I attempt to, it produces the error I've attached below, and places a .mov file on the desktop with a generic icon, unlike the typical icon with the video preview. That file can't be read by Quicktime or VLC and is a far smaller size than it should be.

A little more info

This is happening on a late 2012 iMac running OS 10.15.7 (the last version that's compatible) with videos taken on an iPhone 12 Pro (always with the latest update). I also use a 2020 Macbook Air (always with the latest update) and the same problem doesn't occur. So I'm assuming it's something to do with compatibility between the videos I take on my iPhone 12 Pro and OS 10.15.7. I have the photos app synced with my iCloud account between all 3 devices and side by side, the Macbook Air can do what I need with no issue whereas the iMac can even though it has no issues operating in any other way.

Even more info

I know this may not be typical, but let me describe my workflow. On the 1st of each month, I filter through all photos and videos I've taken from the previous month to correct/edit or delete any necessary. Then I export them all on my iMac, separate photos and videos, and archive them to folders labeled by month and year to the Pictures and Movies folders in Finder. I also then upload them to a photo sharing site that I have shared with family. They also then get backed up with Time Machine to a large external HD. I've done this for many years successfully and like this method as it achieves redundant backups, lets me work with the files in photo editing and video editing apps readily, and lets me easily post to sharing sites. I know there may be other methods of doing all of this, but this has been what I've grown to prefer. It was never a problem until a few months ago. At that time, there was a trifecta of the iPhone 12 Pro upgrade, M1 Macbook Air upgrade, and Big Sur update. Ever since then my photos still export with no problem, but not video. As a workaround, I've been exporting on my Macbook and then transferring to my iMac. However, it's an added step and one I'd like to solve if possible.

If there's any articles that point to where there may be a setting, video format, or compatibility issue that I'm missing, please let me know.