Stanisław Lem's Cyberiad is an easy rec if you like Pratchett and Adams, although I am informed by at least one Pole that there's no substitute for reading it in the original (the English translation is well-esteemed by those of us unfortunates who can't read Polish, at least). Mortal Engines continues in the same vein.
Italo Calvino's Cosmicomics perhaps stretch the definition of SF a bit but ditto.
Octavia Butler wrote a ton of great stuff; I'd probably start with Lilith's Brood or some of her short stories.
Others have recommended Le Guin and The Left Hand of Darkness is indeed excellent but based on your tastes I'd suggest going with the Earthsea books or the short story collection The Wind's Twelve Quarters first. Bradbury too, although maybe The Martian Chronicles over Fahrenheit 451.
JG Ballard might be a little bleaker than you're looking for but Vermilion Sands is probably worth a shot.
Ted Chiang's Story of Your Life and Others is one of the best collections of shorts I've read, full stop. The title piece was the basis for the movie Arrival a couple years ago.
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