I think The Left Hand of Darkness is probably the most agreed-upon science fiction classic. Dune is the “biggest” but it’s alot easier to find people who don’t like it.
I recommend The Dispossessed, but I’ve always been somewhat surprised that it’s so beloved, but it’s not a book you’d read for the plot or characters.
The Lathe of Heave is Le Guin doing PKD. That’s even how she described it. It’s good, so read that one too.

PAY FUCKING ATTENTION BRUH

Well if you think that book is demanding, stay away from Gene Wolfe (of whom Le Guin said “Wolfe is our Melville,” a quote subsequently reprinted on many of his book covers).

it’s likely just an allegory for Vietnam-era white guilt

I think that the message is too broad to tie to a specific historical era, as evidenced by this mediocre and unnecessary 2024 story, which won the Nebula and Locus Awards this year and was nominated for a Hugo:

https://clarkesworldmagazine.com/kim_02_24/

If there is are special awards for diminishing returns it should win that too. I’m sure that if nothing else prevents it from lasting, all of the contemporary references will. You don’t need to read it, just ready the title.

There have been a bunch of “sequels” to that story recently. I read one that was published in Asimov’s a few years ago and was told from the perspective of the kid. I thought it was just lame empathy porn that misses the point of the original.

N. K. Jemisin wrote a story called The Ones Who Stay and Fight, but I haven’t read it.

Le Guin’s really famous story “Vietnam story” is The Word for World is Forest. Alot of people consider it one of the great SF stories, but it’s unusually blunt for her and you can count me as one of the people who think that’s a bad thing. It’s not a bad story but it doesn’t deserve it’s reputation. Many people thought that it was one of the primary inspirations for Avatar. Le Guin herself thought so, and was angry about it.

Of the “Hainish Cycle” books that came out before The Left Hand of Darkness, Rocannon’s World is okay but it’s a more basic adventure story that what she’d do later. The prologue was originally published on its own as a short story, “Semley’s Necklace,” and is one of her classic short works, but the entire novel is less well remembered. Here is the original cover:

The next two books, Planet of Exile (which isn’t really long enough to be a novel) and City of Illusions are more mature.

I’ve read some other shorter stuff, but not the Earthsea books or her other later novels (yet).