They did it in the sixties. And they’re still doing it now.
One of the simplest theories to this conundrum is that it’s an artifact on the lens, or indeed the Moon. ‘Streetcap1’, the YouTuber responsible for the video doesn’t hold with either though, posting a second video proving that it couldn’t be the Moon.
The biggest mystery however is why NASA didn’t just use duct tape to cover it up. That’s what they did before, after all.