To add more details :
Contents slated for theaters and OTT platforms in Korea are under the supervision of the KMRB (Korean Media Rating Board) which is the heir to an old censorship agency. It liberalized considerably in the recent years (15 years ago they were assigned in court because they systematically handed 18+ ratings to LGBTQ content) and is basically now a functionally independent organization that advises and rates content. They do have an exceptional power to rate out of scale a program if it is deemed to cause extreme harm to society or the nation as a whole but it's been almost never used in the recent years. Domestic services such as TVING, wavve, watcha, coupang play and foreign ones like Netflix go through them.
Ratings are done a priori, before broadcast. No large scale diffusion (Movie, OTT content, MV...) can happen without a KMRB rating.
On the other hand, dramas and shows for TV are under the strict purview of the KCC (Korea Communications Commission) through the KCSC (Korea Communications Standards Commission), which is basically an extension of the Korean presidential office right now. As said, they have strict censorship, they handle civil petition, may impose sanctions, and in extreme case even shutdown a station entirely. If you're interested by politics, there's currently a battle between the government and the parliament on its leadership (https://en.yna.co.kr/view/AEN20240821005400315). They also have an indirect say on the content of public channels KBS1&2 and MBC through a foundation. TV stations self rate programs but it can be revised by the KCC at any time.
Ratings are thus revised a posteriori, after broadcast.
tvN is a commercial private TV channel owned by CJ Group through CJ ENM.
TVING is a commercial private OTT service operated by majority shares (48%) by CJ ENM.
All tvN content goes to TVING (there are exceptions).
Not all TVING content is on tvN. This is the case here.