Hi fuzzy257,
If Optimize iPhone Storage is enabled with iCloud Photos on your iPhone, then it's expected behavior to be unable to transfer the file via a cable if the file isn't downloaded to your device. This information is discussed here: Transfer photos and videos from your iPhone, iPad, or iPod touch to your Mac or PC - Apple Support
If you have iCloud Photos turned on, you need to download the original, full resolution versions of your photos to your iPhone, iPad, or iPod touch before you import to your PC.
Here is how you can download the video:
Download iCloud photos and videos - Apple Support
"On your iPhone, iPad, or iPod touch
- On iCloud.com, tap Photos.
- Tap Select, then tap a photo or video. To select multiple photos or videos, tap more than one. To select your entire library, tap Select All.
- Tap the more button
. - Choose Download, then tap Download to confirm.
If your photos download as a ZIP archive, learn how to uncompress the folder on your iPhone, iPad, or iPod touch. "
Apart from the steps above, you can also download the video from iCloud.com on your PC if iCloud Photos is enabled on your iPhone. That way you won't need to transfer via the cable: Upload and download photos using iCloud.com - Apple Support
Let us know if that helps.
Kind regards.