The first drama that comes to mind is "Do you like Brahms?" which had both types of love triangles.

The others to some extent are:
Romance is a bonus book
IOTNBO
Inheritors
Doctors

In love triangle with the woman as center, the second male lead often is very nice but in love triangle with a man as center, it's the opposite. So it happened but the second female lead is often badly written and just not very nice (to stay polite).

Hi, Bye Mama! 😅 Why I'm feel sorry writing this up.

Mr. Queen comes to mind. The Second FL's story was well-written and had a complete arc. Also one of the rare instances where the ML is in love with SFL first and the FL later.

Also Oh My Ghost. How often do you want the ML to end up with BOTH FLs even if one of them is not in this world anymore?

ITAEWON CLASS (Netflix). IC was one of my favorites of 2020 with the triangle being: ML Park Seo-joon and FLs Kwon Nara and Kim Da-mi. It produced here on DramaBeans one of the most vituperative shipping wars since A POEM A DAY (which was the more traditional one woman/2 guys).

As an aside. I thought Kwon Nara’s character was, @kurama points out in her comment, maybe the more badly written but certainly ‘under written’ of the two women. It is my surmise that is why at the end there was the PBG cameo. It was certainly not for the ratings because the ratings were fine for the whole run but as a make up by the Director to KN for the way her character played out.
Lol, as you can tell I was on the Kwon Nara/Park Seo-joon ship.

Aside from dramas other beanies have mentioned, even though this drama is not the best example, "Doctor Stranger" can be one of them.
You may say it wasn't really a love triangle, but i think some viewers experienced SLS. I did.
Lee Jongsuk-Kang Sora chemistry was great

Oh Hye-Young Again
Fight My Way
Suspicious Partner
The Liar and His Lover

Though I feel like at least the first three also had some sort of triangle with the FL at the center, but they either were minor storylines or were just a red herring/misunderstanding.

Before reading this post I didn't even realize how far less common this kind of love triangle is!!
Went through my 100+ watched shows and came up with less than 10 examples!! xD

What I got:
- Dali and Gamjatang is probably the most accurate rec.
- A Piece of your Mind and The Package where the ML loves 2 women (not quite at the same time, though).
- Do You Like Brahms and Crash Landing On You have more of a love square, but still both MLs are liked by 2 different women.
- Oh My Ghost and Mr Queen have a fantasy element so it's quite the unusual triangle, but pretty fun! ...they also have a very polarizing ending and resolutions of said triangle, so there's that! xD
- 100 Days My Prince and Moonlight Drawn By Clouds do kinda apply but not really, since it's more of a forced "love triangle", as expected from Sageuks!

All of these are dramas I generally loved, usually the love triangle is fine, or at least bearable (for me that I'm not a fan of this trope).
Can't say the same for the one in DYLB; I still loved the show, but it gets a little frustrating towards the end in that aspect.

Didn't Nice Guy have a love triangle? I feel like melos have a lot of love angst in general - not sure if you can call them triangles when so many people are involved.... love hexagons?
Usually when two women are in love with the same man in dramas it's the FL and an ex-girlfriend who's changed her mind. (Many examples in the lists above)

I'm not sure but can I mention Brilliant Legacy with Eun Sung-Hwan-Seung Mi love story ??

Go Back Couple
Wild Romance

The female-male-female love triangle in Bad Family isn't central to the show, but it's my favourite - mostly because the second female lead is written as a kind, sensible and honest woman, and also because the interactions between her and the male character are hysterically funny.

Two that come to mind:
The time I’ve loved you/The time we were not in love
Backstreet Rookie

Gaksital (Bridal Mask)

Rebel: Thief Who Stole the People. In my previous comment I mentioned Gaksital. In both dramas the 2nd FL is a tragic figure.

Miracle That We Met!! But technically one of the FLs loves her husband who’s trapped inside the ML’s body though. Another drama I shud say is Marriage Not Dating. ML’s mother and FL fight for ML’s love.

I don’t know if these count cos these are not ur typical love triangle, but I do love both the dramas cos they were well written.

Fated To Love You (the 2014 kdrama with Jang Hyuk and Jang Nara) - although I'm not sure that was done well. The SFL is hardly a kind person and takes advantage of the ML's amnesia 🙄, but she's not a one-dimensional plot device and seems to love the ML, not just covet him. She does become more sympathetic, or at least pitiable, in her uphill battle against the drama's title.

My first K-drama Wuri's Family: Kim Hyo-jin was in love with her childhood best friend Kim Jae-won, but he was in love with the female lead.

She Was Pretty, but like all of these love triangles that aren't done well, you start to hate the second female lead.

Kim Sam Soon! ❤️❤️❤️
Classic one guy-two women.

Mr Sunshine, kind of, although there was a lot of triangulating going on all around 😁

okay, i'm going back to the drama that hooked me on k-drama, 'my lovely sam soon' or 'my name is kim sam soon.' it changes a # of things in k-drama & this is why it will always be my favorite k-drama!

Our beloved summer - It had both type of love triangle but female-male-female was better written. NJ was genuinely smitten with male lead. For second male lead it was just first love/obsession and she was his best friend’s girlfriend. He never acted on those feelings but they never even interacted to warrant those continued feelings.
Oh, my ghost – I am not sure if the ghost was romantically interested in chef but I was quite sure that chef was in love with two different women at same time.
The below drama had unhealthy love triangle and I would not recommend them for the romance.
The scent of woman – The female lead did not even like male lead but was hell-bent on marrying him.
Goong – it had both type of love triangle but every relationship in this show was unhealthy.

Fated to Love You. I thought that one did a great job of showing how the ML could be truly devoted to one woman but then slowly, over time, fall in love with the FL.

Did “The Man Living in our house” have a second female lead? I remember Jo Boa playing her.

Jealousy Incarnate - there were two of them
Fated To Love You
My Girlfriend Is A Gumiho
Sassy Girl Chun Hyang
Get Karl! Oh Soo Jung
Save The Last Dance For Me
Another Oh Hae Young
Familiar Wife
My Name is Kim Sam Soon

To be fair, a lot of the older kdramas have a love square formula

In Our Beloved Summer, almost a love triangle of two men and a dude but one side (the idol) conceded as the OTP reconciled.
Queen for 7 Days, a tragic love triangle for sure.

Actually in all seguk dramas you can find at least two women in love with the king like Moon embracing the Sun, Empress Ki, War of Women, Dong Yi ...

Yumi's cell(also this was more of a crush of two worman on the same man)
Dream High 2, the man was JB
Imitation
Backstreet rookie

I also remember
Man in vail
Beautiful love, wonderful life
Yi San
Love Rain
You are beautiful
When my love blooms
My girl
Playful kiss
My ID is Gangnam Beauty
Boys over Flowers
Dr stranger
Flower boy band
The smile has left your eyes
Reply1988
Alice

There are also
Crash landing on you
Cheese🧀 in the trap

The only ones that haven't been mentioned are my favorites.
Well, their actually love squares, but they all start with the 1 guy 2+ women dynamic.

The Man Who Can't Get Married: 3 women, 1 guy. One of the most hilarious love squares ever.

Protect the Boss: starts with the 2 girls 1 guy (and 2 guys 1 girl) trope, and then it becomes 1 couple, 1 womence, and 1 bromance. Iconic.

The Producers: I don't know if it counts tho, for me Hyo Jin's characters always liked the other dude (Tae Hyun's character).

Ps. Not the 2 girls 1 guy trope, but another amazing love square is Ho Gu's Love.

Too many to list!

Coffee House which is one of my favorite dramas. I watched it after the release but to my understanding not all fans were happy with whom he ended up with in the love triangle. I loved it.

Crazy Love
Jinxed at first (not the main plot)
Woori
Kiss sixth sense
Alchemy of the souls(defently will have several love triangles)
Thirty Nine

Oooooh I love this concept :D