You could easily fake a document and post it on twitter. You could fake a photo of putin pointing a gun at ukrainian children easily. What's so different with a video?

The same thing we already do with photoshops and video edits.

(Upvote or downvote.)

Do you think that banning a subreddit will stop that from happening?

If Putin wants to threaten someone, it's on him to make the other party believes the threat. Hopefully Putin has more trustworthy methods of communication than posting videos on Twitter. Like having his ambassador deliver the message in person, or at least confirm it.

When this doesn't happen, the recipient can be assured that the threat was either pure PR or fake. In either case it can be ignored.