Not a Lawyer.

I'm wondering if a false DMCA notice is a form of slander/libel?

Oh dont worry, I am sure viz media tries to DMCA them regularly.

haha so did I and then wondered if they had unfeasibly large testicles

Most likely it is just automated and matching text, which should be illegal.

I found before that the company that does this apparently is just one person with an AI agent, because they ("Remove Your Media LLC") give a street direction but there's... Only a Walmart.

From what I know there are a lot of fraudulent "companies" that are sending false DMCAs to anyone and everyone on YouTube (the channel deephumor is documenting them). They're copyright claiming on behalf of people they aren't even authorised to act on behalf on. They copyright claim people just talking about anime, no clips from animes, just talking. Whether they're actually authorised by Viz media or not, who knows. There's this Remove your Media, there's also another called The Media Entertainment or something just claiming stuff as their own to silence critics. YouTube just allows them all since it's just run by bots now.

The notice at the bottom is the one sent by them, and people that recieve them are allowed to share them publically.

#Yes