Matt Birchler shared a macOS terminal command to remove the play button on icon-sized video files:

defaults write com.apple.finder QLInlinePreviewMinimumSupportedSize -int 99999

Then restart the Finder by running killall Finder and the change will be in place.

And it doesn’t affect Quick Look:

And don’t worry, this does not impact the ability to hit spacebar on an icon to see a large preview of it.

I’ve never been bothered by the ability to watch videos at postage stamp size, and actually thought it made a fun demo of macOS’s whimsy back in the day. But good to know you can turn it off.