Restoring Thumbnail Previews in macOS Revision as of Monday, 19 December 2022 at 18:40 UTC

Got generic-looking icons instead of previews for MP4 files and couldn’t figure out what was going on.

Tried Finder -> View -> Show View Options -> Show icon preview to no avail

Then force quit com.apple.quicklook.ThumbnailsAgent in Activity Monitor and relaunched Finder. All was well.