Quite a few popular dramas in the last few years seem to be adapted from books - both Korean and Chinese.

My favourites would be Through the Darkness (based on a non-fiction book by Korea's first criminal profiler) and Reborn Rich (based on a web-novel The Youngest Son of a Conglomerate).

Among older classics, Coffee Prince was based on a novel iirc. Also Goong was based on a very popular manhwa (you can actually see the FL with copies of the manhwa in the latest episode of Love Next Door lol)

Sungkyunkwan Scandal it was based on The Lives of Sungkyunkwan Confucian Scholars novel. The writer wrote the novels for Moon Embracing the Sun and Lovers of the Red Sky too.

I didn't read the original novel but liked the drama :

Girls' Generation 1979 It was a short drama based on a novel (same title) by Kim Yong-hee.

The Interest of Love It based on the novel with the same title by Lee Hyuk-jin.

Kim Jiyoung born 1982 is a film based on a novel
Lovely runner is based on web novel Tomorrow is best

When I googled this before the ones that surprised me were:
I will come to you when the weather is fine.
Hello me based on a novel Fantastic girl
Mrs Hammurabi
Flower crew: Joseon Marriage Agency
Temperature of love based on the novel Good soup never picks up the phone
Once upon a small town

I think my favorite recent one has been The Kidnapping Day based on a novel by Jung Hae-yeon with the same name. No idea how faithful it is, but I’d love to hear your thoughts if you read and watch it back to back! Yoon Kye-sand and Yuna were totally great in this drama.

The Red Sleeve was based on a novel, although I don't know if it's available in an English translation.

Hwayugi (A Korean Odyssey) is based on the classic Chinese novel Journey to the West. I highly recommend the recent translation by Julia Lovell. Here's good review:

https://lareviewofbooks.org/article/a-chinese-classic-journeys-to-the-west-julia-lovells-translation-of-monkey-king/

Kdramas:
- Our Blooming Youth is based on the Chinese novel, ”The Golden Hairpin" (簪中录) by Ce Ce Qing Han (侧侧轻寒)

- Scarlet Heart: Ryeo is a remake of the C-drama Scarlet Heart (步步驚心), which is based off of a Chinese novel, Startling by Each Step, by Mo Bao Fei Bao 墨宝非宝

Those are just the few from the top of my head for Kdramas, but for a longer list, here:
https://en.wikipedia.org/wiki/My_Sweet_Mobster

As for C-dramas (from what I’d recommend):
- The Untamed (陳情令), based off of the webnovel ”Founder of Diabolism” (魔道租師)

- One and Only (周生如故) & Forever and Ever (一生一世) — basically 2 dramas loosely related but based off of the same book, ”One Life, One Reincarnation” by Mo Bao Fei Bao 墨宝非宝
(Translated novel here: https://www.novelupdates.com/series/one-life-one-incarnation-beautiful-bones/)

- Lost You Forever, based off of a novel of the same title (長相思)
(Translated novel here: https://www.novelupdates.com/series/lost-you-forever/)

BUSINESS PROPOSAL is inspired from a manhwa, and a real good one at that.

Come Back, Mister is based on a novel by Jiro Asada. This drama came out at the same time as the big drama Descendants of the Sun. The poster and plot for DOTS didn't catch my interest and the reviews trickling in were tepid. Instead I was watching Come Back, Mister. A relative who studied Korean in college was watching Descendants of the Sun but admitted it wasn't that great, so I told her that I was watching Come Back, Mister and enjoying it alot. So she watched it and said it was really good! Highly recommended drama. The novel title in English is "Mr. Tsubakiyama's Seven Days". It was also made into a movie.
It's not always the case, but the general impression I get from novel and comic based dramas is that the plots are a lot more complex in a good way and the endings are (or should be) better. Overall everything is better constructed and higher quality. As a student of poetry, for me, the hardest part to get right is the last line. So I'm way more excited about a drama when I hear that it's based on a novel or comic.

There are a lot of dramas that are so good that it feels like they could have been based on novels. Three examples: Stranger, Goblin, Attorney Woo.

Cinderella, every kdrama...

There’s a slew of dramas based on books and other literary sources; in fact, it seems like there are far more adaptations than original screenplays. Here are some of my favorite dramas adapted from novels, none of which I’ve read. (I didn’t include webcomics or web novels.)

365: Repeat the Year - adapted from the novel Repeat, by Kurumi Inui
Move to Heaven - adapted from a collection of essays by Kim Sae-byul called Things Left Behind
When the Weather is Fine - based on the novel of the same name by Lee Do-woo
My Lovely Boxer - based on the novel Pure Boxer Lee Kwon Sook, by Chu Jong-man
Recipe for Farewell - based on the book It Might Be a Little Spicy Today, by Kang Chang-Rae
The Interest of Love - based on the novel of the same name by Lee Hyuk-jin
Poong, the Joseon Psychiatrist - based on the novel Joseon Psychiatrist Yoo Se Pung, by Lee Eun-so
Lies Hidden in My Garden - based on the novel of the same name by Kim Jin-young
The Secret Romantic Guesthouse - based on the novel Flower Scholars' Love Story, by Kim Jeong-hwa

A Love So Beautiful is based on a Chinese novel (I read an unofficial translation of it!) I think it's an actual novel and not a webnovel, but I could be wrong

How about Little Women - not based on but inspired by?

Though the story is vastly different, it remains a tale about sisters with different personalities struggling to find their respective ways out. To me, it’s an outstanding twist of the classic novel.

All of Gu Man's novels that have been made into c-dramas, including You Are My Glory, Love O2O, You Are My Sunshine, Boss & Me.

Mo Bao Fei Bao novels that became c-dramas Amidst a Snowstorm of Love, Love Me Love My Voice, Go Go Squid, One and Only, Forever and Ever.

Jiu Xiao Qi novel that became c-drama Skate Into Love.

Jiu Lu Fei Xiang novels that became c-dramas The Legends, The Love Between Fairy and Devil, The Blue Whisper, Back From the Brink

Tang Qi Gong Zi novel that became c-drama Eternal Love.

Zhu Yi novels that became c-dramas Hidden Love and When I Fly Towards You.

Qiao Yi novel that became c-drama Le Coup de Foudre

Twentine novels that became c-dramas Lighter and Princess, Falling Into You

Zheng Yi novels that became c-dramas Love Like the Galaxy, The Story of Ming Lan

Qiao Yao novels that became c-dramas Everybody Loves Me, Love Scenery, Only For Love

Ding Mo novels that became c-dramas Memory Lost, Love Me If You Dare, When a Snail Falls In Love

Xian Cheng novel that became c-drama Go Princess Go and k-drama Mr Queen

Zhao Qian Qian novels that became c-dramas Put Your Head on My Shoulder, A Love So Beautiful, Love Equations

Shi Jing novel that became c-drama Story of Kunning Palace

I would say "Joy of Life". That's a wonderful Cdrama, worth watching.
I watched the first season and the cliffhanger ending made me scramble for the book and read it till the end.
The second season ended a month or two ago. There are some changes between the book and the drama, some good, some confusing as I forget what I read ...