Now for some of the points raised by cloa.
Red is such a non-person that no one even his mother doesn't know even if he is a boy or a girl
You're thinking of Professor Oak, not Ash's mother, plus the intro section isn't really meant to be taken as happening in universe.
But if you really want an in-universe explanation for that, it's either because he's old or it's implied to be an unfunny grandpa joke (if we extrapolate what Blue says about Oak in LGPE at least).
Is any proof that he is anything but a grinder pokemon trainer- one that never plays or never treats pokemon with any respect?
Grinding isn't really a thing within the Pokemon universe.
It's a game mechanic that's there because it's a game, it's never been a part of any non-game representation of the Pokemon universe.
Plus, this isn't how the burden of proof work, if you want to make an allegation you have to bring proof yourself (in this case, you need to prove Red's a grinder) instead of asking people to prove the opposite.
I think he doesn't speak because he despises pokemon (that don't help him win very fast)
I've already addressed the ableism but the reason he doesn't speak is because he's a character from a JRPG in the 90s that's supposed to be a character surrogate.
It's not deeper than that. Further depictions didn't have him speaking or have shown him to have a distate of speaking because RBY set the tradition that the character was silent.
If you really want an in-universe reason that are plenty that are more likely than "he hates Pokemon" (which doesn't even make sense because Pokemon can't talk, he'd be not talking to people), such as: disability (talking might hurt or be uncomfortable), social anxiety, neurodivergence, etc.
That being said, "Red is silent" is revisionism. Red did talk in the original games, the game just didn't show it to you. The proof of that is that Copycat "copies" what Red (or Gold or any other protagonist for that matter) is saying and the game shows that and Copycat does say she's copying the player.
But Red being silent stuck in the general mind despite it just being a game limitation of the time / a character surrogate thing so TPC went with it.
Also, Red has an Espeon in GSC. That's a friendship evolution and the designated "I despise Pokemon that don't help me win very fast" character of those games explicitly could not get a friendship evolution until he discovered that was wrong, actually, so your theory doesn't carry a lot of weight.
Or the Pokemon games have no nearly no friendly interaction options with Pokemon- hence it says something about Red too ?
Early Pokemon games have nearly to no friendly interaction options because they were made for hardware that has less memory than a toaster.
It says absolutely nothing about the characters.
I just read Red's first words "Words are unnecessary Let the Pokemon do the talking" - confirming to me that he is piece of work. Pokemon are for battling with.
Those are two separate lines, and you're not taking the context of either in consideration. Not to mention the two whole other lines / scenes in between those.
Flint asks "How do you give commands to your Pokemon in battle without talking?"
The Masters player says "Maybe they understand each other without words?"
Red looks at Charizard, then jokingly say "Words are unnecessary."
Red's saying "I'm so close to my Pokemon that I don't need to say words, they just know me that well."
I can't find the exact context of that second line you mentioned of "Let the Pokemon do the talking." anywhere in an easily searchable format right now, but if I had to guess, the context is that it's being said right before a battle.
It's basically the Pokemon version of "Let the ball do the talking" or "Let's talk with our fists." that shows up occasionally in shounen manga / anime or cheesy sports stories.
Red became champion because he can grind through battles and everything is handed to him.
Again, grinding isn't really a thing outside of actual games. There's no reason to believe he did any grinding or that grinding or levels are a thing outside of the videogame representation of Pokemon.
Even if they are things, grinding's basically training, and from a game perspective, it increases the Pokemon's bond with the trainer. That wouldn't even be a bad thing.
Plus, Red got pretty much nothing handed to him in the games outside of a few gift Pokemon? Red's final team is widely inspired by Ash and not actually representative of a team he could feasibly get before like LGPE, (in which he could feasibly capture all of those Pokémon by himself).
