Is "Too Much People" possible when I want to get the feeling of uncountable people?

In general, use many when you can count and use much when you can't. For example:

There were too many people in the same room.

You can count the number of people in a room.

There was too much dressing on the salad.

You can't count salad dressing.

You could say "too much of a crowd". Otherwise, I don't think there is a nuanced answer to this question. If you want to say too much "people," then you're not referring to the number of people in the room. Use a word that more accurately describes what you are referring to so that everybody understands the point you're trying to make. For example, do you mean too much testosterone? too much snobbery? too much attitude? too much body odor? too much ego? Most readers will interpret "too much people" as a mistake, not as some nuanced phrase with hidden meaning (unless it's poetry and then you can do anything you want).

In a nutshell, under no circumstances that you can substitute "much" for "many" when it comes to counting people. However, this rule may only applies for modern English, since they can be found in some of the old books. Here is a phrase from the Geneva Study Bible that I came across when I was searching for clues to answer your question:

"For I am with thee, and no man shall set on thee to hurt thee: for I have much people in this city"

You can read more about this phrase here: http://biblehub.com/kjv/acts/18-10.htm

Native speakers can sometimes stretch the boundaries of English with usages that violate the grammar we all usually follow instinctively, but that nonetheless manage to mean something with that violation. I could imagine a native speaker saying "There was too much people in there", with stress on the word "people", to convey that (s)he isn't seeing the people as individuals, but as a mass of bodies — a confusion of arms and legs and torsos and heads — taking up physical space, pressing in too close. (This is essentially the cooperative principle, but applied to syntax rather than pragmatics.) A more common (and grammatical) way to express the same thought might be, "There were too many bodies in there."

Alternatively, I could imagine a native speaker using "too much people" in a somewhat humorous way; if one person says, "The arguments were insane. There was too much testosterone in that room", I could imagine someone replying: "It's not a testosterone thing, it's a people thing. There was too much people in the room." Here the use of "much" doesn't affect the meaning at all; it's just an abuse of grammar to parallel the use of "too much testosterone", while lightening the tone a bit. (If played up a bit, it could be a mild dad joke.)

But in either of the above scenarios, if a non-native speaker said the same thing, it would just sound like a mistake. Several of my coworkers are native Chinese speakers with imperfect English; if one of them said "too much people", it would seem obvious to me that they simply meant "too many people" and got their grammar mixed up. If they were intentionally using "much" for the sake of humor, or to suggest something special, it would be totally lost on me.

(By the way, note that it would have to be "There was too much people", not *"There were too much people", because "much" is only used for singular mass nouns. Stretching grammar is one thing, but there are limits!)

You can use it, in poetic sense, meaning: These people are too much for me. There's too much of people in here. Like Benedetti uses it in this story> http://literaryechoes.com/blog/2017/01/28/idyll-by-mario-benedetti/