It's quite old: The Black Company by Glen Cook

Have you read Discworld? It’s a bit more fun than The Witcher but has similar twists on traditional fantasy and magic ideas

I have no idea if it’s actually similar, but I googled it and there seems to be an overlap of fans between Farseer and Gentlemen Bastards.

So I’m suggesting The Lies of Locke Lamora! The narrator adds a whole extra layer to the disguises, if you’re into reading by ear

old school: Forgotten Realms

More games of thrones-ey, but less so: Wheel of Time

Grand but well paced: Stormlight Archive (Brandon Sanderson)

scifi one-shot: Sea of Rust

If you want more grimdark and it has to be fantasy, check out Warhammer horror especially the vampire Genevieve. If you’re okay with grimdark science military science fiction, a good chunk of the Warhammer 40k and Horus Heresy lines will fit your bill.

I feel like Hobb is much lighter. For whatever reason I always think of Tad Williams and the Dragonborn Chair as connected to Hobb. I suspect it’s from the Legends anthology but they were only together in Legends II with a different Hobb trilogy setting and Otherland for Williams. Both are great starting points to find authors that have huge bodies of work that could hook you. They were how I found George RR Martin back in the early aughties.

i got one no one seems to have heard of, but its a series by a bunch of writers, and it was stitched together by none other than George RR Martin..

The WildCard series... i just love the different writing styles across the different characters...and its an amazing universe.. i highly recommend it

https://en.wikipedia.org/wiki/Wild_Cards

the short is: alien race f's up a non trivial percent of the human population with a virus.. most die. what neat is the mish-mash of history with a new minority of deformed humans. i think it starts in ~1947 running through the 90s.

British writer Neil Gaiman met with Martin in 1987 and pitched a Wild Cards story about a character who lives in a world of dreams. Martin declined due to Gaiman's lack of prior credits at the time. Gaiman went on to publish his story as The Sandman.

Got a preference for light or dark?

I always liked the Krondor series. It inspired several D&D characters of mine. Like The Witcher, it too has a video game based on it. Though it's from way back in the day on DOS.

Green Bones by Fonda Lee

First book is Jade City. I like that it's set in a 1950's tech world with the magic being only one part of the greater story. Crime, politics, family drama; it's the Godfather with super powers.

To Your Scattered Bodies Go... by Philip Jose Farmer. Everyone who ever lived wakes up on the banks of The River.

The Prince of Nothing series.

A very solid series, dense as fuck, with an intriguing way magic works. Just be aware that there can be a fair bit of talking in-between action scenes, there's a lot of time spent in political/religious discourse between characters.

Also, birds with human heads! A prostitute finding out who she slept with by the fact he literally has black cum! Too many scenes of people cleaning themselves up after taking their morning shit!

If you liked Assassin's Apprentice, Robin Hobb wrote a lot of other excellent books set in the same world.

Empire of the Vampire was great if you want something like The Witcher.

The long price quartet

The Malazan book of the Fallen by Steven Erikson would be my recommendation. Start from Gardens of the Moon and go ahead... It keeps getting better and better!

Pale Lights, an ongoing web serial set in the pistols-and-sabres era. The first book's already out for you to read! The author previously wrote A Practical Guide to Evil, which is completely finished.

Some slightly off-track suggestions (because genres are a bit misaligned with what you're asking for):

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Gideon the Ninth by Tamsyn Muir (The Locked Tomb series)

Brought up by unfriendly, ossifying nuns, ancient retainers, and countless skeletons, Gideon is ready to abandon a life of servitude and an afterlife as a reanimated corpse. She packs up her sword, her shoes, and her dirty magazines, and prepares to launch her daring escape. But her childhood nemesis won’t set her free without a service.

Harrowhark Nonagesimus, Reverend Daughter of the Ninth House and bone witch extraordinaire, has been summoned into action. The Emperor has invited the heirs to each of his loyal Houses to a deadly trial of wits and skill. If Harrowhark succeeds she will be become an immortal, all-powerful servant of the Resurrection, but no necromancer can ascend without their cavalier. Without Gideon’s sword, Harrow will fail, and the Ninth House will die.

I must admit that Charles Stross' pitch is what got me to pick up the book in the first place, it's just too funny:

“Lesbian necromancers explore a haunted gothic palace in space!” —Charles Stross

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The Final Empire by Brandon Sanderson (Mistborn Trilogy)

OK, maybe not so far off the path ...

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Storm Front by Jim Butcher (Dresden Files series)

Prince of Thorns by Mark Lawrence is the first book of a very dark trilogy.

I will also add this, even if it doesn't match the request, but because it's so weird and funny: Shades of Grey by Jasper Fforde. It's about a quite absurd society where people's social status is determined by their ability to perceive colors. And they are not allowed to manufacture spoons. Sci-fiish