I get that Star Wars is space opera and science fantasy, so I don`t care that much if all planets mostly consist of one type of environment or that most alien species seem to have only one etnicity, culture and language.
And come to that, they aren`t very alien, they are mostly all human. They have eyes, ears, arms, legs, audible languages, two genders, even human gender roles, human values, vices and desires and so on.
It`s fine, it is science fantasy and space opera after all! "planet of hats" makes it all very clear and easy to picture and keep track of.

Are there any well known planets in the Star Wars Galaxy that aren`t one note and doesn`t feel more like small countries or cities than planets?

And are countries even a thing in Star Wars, or is it just a planets and cities type of Galaxy?.. Are there known planets as diverse or even more diverse than earth?

Are there intelligent aliens that have more than one language or culture or that aren`t just weird and alien looking versions of humans with a few alien qualities?

Again, it`s fine, this is space opera and fantasy, so like elves and dwarves, aliens are just extremes of human culture, I get it.

Are there intelligent aliens that have more than one language or culture or that aren`t just weird and alien looking versions of humans with a few alien qualities?

You'll have to look but they exist. The Huk are in the film, though probably not quite what you had in mind.

The Ugors are better. Though they still typically represent themselves at 2 arms/2 legs/ect.

The Ergesh are probably closer, they have no arms, legs, different biological functions.

Revwiens may work for you as well as they aren't even in the animal kingdom.

But yeah, most of what you see in the films are limited to forms an actor can be squeezed into...

Are there any well known planets in the Star Wars Galaxy that aren`t one note and doesn`t feel more like small countries or cities than planets?

If you dig through the old WEG planets collections, campaigns, ect, you'll find plenty. The thing is they rarely talk about anything but the one that matters.

You don't need to describe every little two-bit one horse town on a planet where one major city and two special points of interest will do. Likewise the largely uninhabited polar region, is just a place that the players aren't likely to visit.

Imagine if Earth was in Star Wars. You likely wouldn't talk about every major city, region, ect. You'd pick the two or three the players are most likely to visit.

And are countries even a thing in Star Wars, or is it just a planets and cities type of Galaxy?.. Are there known planets as diverse or even more diverse than earth?

They are, but they are by nature rather rare, or are not worth mentioning.

Colonies that are formed with full knowledge of galactic civilization will be unlikely to for separate nation-states, because they know that the operate on the galactic stage they will need a single unified voice.

New discovered worlds that have nation states will also eliminate them, or present some other front for the same reasons. Again, if you looked at Earth the galactic database would probably rate it as a Bureaucratic Representative government based off the UN being the combined "government" of the planet. Not accurate by Earthling standards, but if the Empire wants to do business on Earth they'd probably have to go through the UN at some point, even if they were only concerned with Chinese mining operations.

Are there any well known planets in the Star Wars Galaxy that aren`t one note and doesn`t feel more like small countries or cities than planets?

And are countries even a thing in Star Wars, or is it just a planets and cities type of Galaxy?.. Are there known planets as diverse or even more diverse than earth?

Read X-wing: Starfighters of Adumar. It's Legends/EU but it shows/explains why the New Republic dealt with unified worlds. These worlds may still maintain their predecessor nationalities but most of the citizens will identify with world rather than the nation. In this sense, the worlds themselves are nations.

Thanks, both of you:)

Naboo has at least three environments that we see (Swamp, Meadow/grassland, Ocean). I generally assume most planets have a variety of terrain, and the "Terrain-Planet" is just identifying what's interesting about it. A Forrest Moon has a lot of forest for a terrestrial planet. A Desert Planet has a lot less water, etc. It doesn't mean you can't find a meadow on Endor, it's just not the first thing someone to who saw Endor would talk about.

Nations is Star Wars would generally be a lot like Counties - they matter for governmental & legislative issues, but to anyone not from that area, they're irrelevant. Regional or national differences on a planet are likely the same - they matter to to the people who live there, but to galactic society they're pointless.

The Mandalorians (TCW) provide an interesting note on this, as we have three faction who do not recognize the authority of the others, and the Republic specifically selects one of them to be the one they recognize as the sovereign state of that planet. There's no reason this couldn't happen elsewhere.