Commiserations! Thank you for trying.
If you use Time Machine ... there may be an "auto-saved" copy of the video at some point.
Else:
If you haven't tried this tip below, might be worth a try:
In Finder > Hold down Command and Shift, then tap G.
In the box that appears: paste this link: ~/Library/Containers/com.apple.QuickTimePlayerX/Data/Library/Autosave Information/
Look in the folder that opens for your video, (use the time/ date created if there are many files in there)
or
A last ditch effort may be searching Mac for "untitled" files in a finder window