How to prevent Spotlight from playing YouTube videos when I paste a YouTube URL into Spotlight When I copy and paste a YouTube video URL into Spotlight (CommandSpace), it automatically starts playing that YouTube video in a miniaturised web browser embedded in Spotlight.
How do I turn off this behaviour? In fact I would most prefer to completely get rid of that embedded web browser entirely.

The reason I often paste stuff into Spotlight is that I use it like a second clipboard/storage space for text.
It's really convenient, a single keybind away. I often paste text there if I have to copy/paste something else intermittently, or need to be reminded of something a few moments later.
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: