[Sorry there's some redundancy-I had to work and didn't get all the links so left this sitting here half a day!]
tvN D Story (webseries like TRAP): https://www.youtube.com/channel/UCLQ_lTDcNOj7VzNeW0kZ17w
Dingo K-Drama: https://www.youtube.com/channel/UC9_XmEfjzwIsXLehscbhbmw
Playlist Global: https://www.youtube.com/channel/UCid83oPnsL-4ZEo8CyQr6Rg
There are multiple Playlist pages; this is the one w/the original series I recognize but the others may also be relevant (there are links to their others on the right side-featured/partner channels). This one, for instance, mostly has BTS but also has a webseries on it: https://www.youtube.com/channel/UCWh7Y7qan9WNxXOucn15O3A
The next 4, Whynot TV pages, I don't quite understand the multitude of-why is Real High School Romance on a diff page from Kiss Goblin, etc? All the same people, though, just like the Playlist/Teenwhy
KOK TV: https://www.youtube.com/channel/UCybPxZoFDPR1qbN04daAc2g
KIK TV: https://www.youtube.com/channel/UC_ZGfQ1Iw9uk8Avr8ohjSdg
리얼:타임:러브 (Real:Time:Love): https://www.youtube.com/channel/UC8DdZkTABAnSBvoRknqOTOA
Whynot TV: https://www.youtube.com/channel/UCw2LXKY_0FbI8-BS4qf-bHg
Lifetime (yes, the cheesy women-aimed TV movie station one but now they do young woman-geared webseries and probably more in SK): https://www.youtube.com/channel/UCNK0-1KNIwowKzZu6tSjqsw
Not sure what you'd do with shows that are here and have their OWN channel on YT ie Bora Cafe/Bora Dabang ( https://mydramalist.com/63411-borabang ): https://www.youtube.com/channel/UCiV292QOaU9tTXMYegByDGA
What about Seezn? I see shows always promoting early episode releases there: https://myseezn.com (https://myseezn.com/html/product.html shows some networks they work with but they also do stuff that will be on vlive/naver/YT a week later.)
I'm sure it's already somewhere but vlive: https://www.vlive.tv/