J4 is LeBlanc confirmed

She doesn't have interactions with J4, at least, not that are in that video. He's just used to demonstrate the lines she has for imitating dudes.

Thaaaaat does not confirm anything.

Jarvan has stated he does not want to be king and that he wants to help is people in what he believes is a better way.

He is king/going to be king, but he doesnt want to, thats one way he isnt himself.

Also didnt riot say that theory was a misconception? Like Vi and Jinx being sisters? (Because they arent)

The only lines in that video where Jarvan IV is present, you can see at the top-left corner it says that the conditions are:

MIMIC ANY MALE CHAMPION

FIRST ENCOUNTER - ANY

So, clearly, Jarvan IV is just being used as a generic (male) Champion in either case. Regardless, even looking at those lines, it doesn't offer any hints about Jarvan "not being himself" or "something strange" happening to him:

Mimic Male Champion lines

"Male sho'ma feels...strange..." "Looking like boys is. Um...Takes getting used to." "Do I smell as bad as I look? ...Yes."

Generic First Encounter lines

"Hello enemy!" "You are not secretly Neeko...Are you?"

The quotes only reference the fact that Neeko sometimes is unsure if she's actually looking at someone, or looking at someone who can mimic her life-essence/appearance (in the case of the generic First Encounter lines), and the rest don't hint at anything, either.

TL;DR:

Neeko doesn't have any special interactions with J4, J4 is just used in those videos as a generic male Champion (makes sense, given she has an interaction for mimicking Garen)

Grasping at straws my dude

Wouldnt Sho'ma be a metaphor for the sex organ?