My current favorite is still:
WHAT ARE WE by: HA SUNG WOON (Love Next Door) 

My Spotify list is still in process, but I've collected quite a few OST favorites here:
OST Favorites (on Spotify)

Oh, I like that one so much.   The OST collection (which I'm still building) is also mixed into my main listening collection.  The different memories that are evoked from these songs, if strong enough, will lead me right into a re-watch.   <3

The wounds of Time. From Marry my Husband 

Cold. Shining for one thing 

Wake up. It's okay to not be okay 

Blown away. School 2015

My turn by Park won. Ending again.

damn here i am with good question 

what is the meaning of OST?

i thing this is means by song but like is there specific type 

2000s OST:

• From The Beginning Until Now - Ryu | OST of Winter Sonata (2002)
• I Believe - Shin Seung Hun | OST of My Sassy Girl (2001)
• I Miss You - Kim Bum Soo | OST of Stairway to Heaven (2003)
• If - Taeyeon | OST of Hong Gil Dong (2008)
• The Day You Come to Me - Kang Chul | OST of Hotelier (2001)

2010s OST:

• Back in Time - LYN | OST of The Moon That Embraces The Sun (2012)
• Crazy of You - Hyorin | OST of The Master's Sun (2013)
• Hope is A Dream That Doesn't Sleep - Kyuhyun | OST of Baker King, Kim Tak Goo (2010)
• If It is You - Jung Seung Hwan | OST of Another Miss Oh (2016)
• Stay with Me - Chanyeol, Punch | OST of Goblin (2016)

2020-2024 OST:

• Drawer - 10cm | OST of Our Beloved Summer (2021)
• Every Second - Baekhyun | OST of Record of Youth (2020)
• Gravity - Jongho | OST of Reborn Rich (2022)
• Sudden Shower - ECLIPSE | OST of Lovely Runner (2024)
• Unable to Love - Doyoung | OST of Dear X Who Doesn't Love Me (2022)

 Ella the Carat:

Original Soundtrack  [ At least that's what I've always understood it to mean xD ]

All you need is to add the movie/drama title  and OST in YouTube's search window and voila.  Makes it super easy to know all the details, so from here, if you want, you can search on your music streaming platform. :)

Ohh so my guess was right

Do ost are sung by actors in drama

Breaking down - Ailee ( Doom at your service) 

See the light - Lim Hyunsik ( When the phone rings) 

Crossroad - Sunmi ( The judge from hell) 

Here with me - Doyoung from NCT ( See you in my 19th life) 

Last chance  - So Soo bin ( Queen of tears) 

A day - Jongho from ATEEZ ( Lovely runner) 

Once again  - Mad Clown, Kim Na young ( Descendants of the sun) 

Pray - Klang ( Angel last mission : Love) 

And many more....