Is "The American people" a redundant saying?

No, "the American people" is a common phrase in US English. I'm assuming you're thinking that it could just be "American people," and that's a good intuition. "American people" is grammatical in sentences such as, "American people love fast food and highways." But again, "the American people" is a fixed phrase that simply means "the US public."

There's a fraction of people fighting another fraction and another fraction doesn't know what to do.

No. This is a meme format, or variety I suppose, where a normal image featuring some sort of scene (of nearly any variety) has the subjects (Spongebob characters in this case) labeled as to make a comparison with something else. In this case, Mr. Krabs is choking out Patrick while Spongebob looks on in horror and Squidward doesn't care. In this meme, the author is making the comparison that every character in this scene is analogous to the American people, or more accurately, sections of it. It's a commentary that the American people are fighting amongst themselves, and there are those horrified and unmoved by the phenomenon. There's also a meta joke here, because normally this meme format has each character labeled something different, but here they're all labeled the same. So it's not redundant, each label is individually communicating something, and its repeated use is intentional. The title of the post "Their plan: Divide and Conquer" goes even further to say that American infighting is an intentional scheme by "them", and who "they" are will depend on their political position and who the bad guy is, but most broadly people will blame the U.S. Government and U.S. mainstream media. Finally, if you're saying that the phrase "The American people" in of itself is redundant, then no. "American" and "people" do not mean the same thing at all, lol. Americans are people, but not all people are American. I guess they could have just said "Americans", but "The American people" is a fixed phrase meant to refer to the American public more broadly, and is usually used in socio-political contexts.

No, it has a certain popular context.

not so much redundant as just inaccurate and wilfully ignorant of basic geography unless it’s referring to the people of the whole landmass (named after the white invader) as the US isn’t all of america as much as they wish they were and the centre of the planet and ever-growing multiverse…

you could say “Americans,” but “the American people” is a very unifying term that implies a single unit comprised of every American, rather than a random selection of people who are American

It’s an oxymoron.

In what way do you think it might be?

Nope! It's literally like this right now ...among the American people

No. There are lots of people who are not American. There are lots of American things that are not people. To specific that your comment (or cartoon) is about the people of America, you would have to say, "The American People."

It’s a joke that this whole country is chaos, some people fighting, some people watching, some people don’t care

Meaning aside this meme is hilarious… You have found something very very good. The American people just refers to the people of America/the United States/ (whatever my country has like 15 valid names in colloquial speech you get it) as opposed to say the people of Britain or the people of say Thailand or china Now whether an article can stand infront of the nationality of the people in a phrase is both contextual and dialect specific. For me it’s “the American people” but for china for instance it’s simply “Chinese people” I can’t entirely tell you why it just is in my dialect.

"American people" does sound kind of redundant. Most people would just say "Americans". However, "The American people" actually means something a little different. It's something people usually say when talking about politics. It means all (or most) of the people of America, as a group. Politicians say it when talking about what the American people want, or how the American people feel about something. That's actually part of the joke here. Everyone in America is attacking everyone else in America, while everyone else in America watches in fear, and everyone else in America is just trying to get through their day in the background.

"Americans" could have worked but this seems more natural to me given the context

No. "The american people" is a collective for "americans"/people of america. Its a joke saying the people of america are fighting each other and are in a state of dissaray. Its saying some americans are like fighting each other like Patrick/Mr.krabs while others are bystanders watching, either concerned like spongebob or indifferent and just done with the whole situation like squidward.

I‘m an American with an American passport. I haven’t set foot in America in over a decade, but if you talked about Americans, it would include me. John is an Irish citizen and has lived in America for 25 years. He is not an American, but he is included in the American people. Does that help?

Its common for politicians

Personally I would have wrote ‘americans’