How to prevent Spotlight from playing YouTube videos when I paste a YouTube URL into Spotlight
With macOS 10.15 Catalina, as a workaround, you can first type a character and then paste the URL to fool Spotlight and prevent it from displaying a Quick Look preview. After editing the URL, you just need to pay attention not to copy that first character.
With macOS 11 Big Sur, none of that is necessary, as Spotlight no longer displays a preview: