Looks like it's even more complex than that:
, it’s pretty easy to take for granted how simple most character and IP rights are from the outside perspective. Take for example DC Comics, Warner Bros. Discovery owns all of those characters and uses them in comics, movies, shows, and countless other places. Universal Pictures has owned the...
comicbook.com
Basically the novelization -- and therefore, in effect, the character of King Kong -- is in public domain, and can be used as the basis for any KONG project as long as elements from that book are included and permission is granted by the Merian C. Cooper estate. And individual studios can then own trademarks that make their versions/interpretations of the character unique and distinct.
The 1933 film is still fully controlled by WB until (at least) 2029. Then it seems like it might enter public domain, meaning that visual iconography and elements specific to that movie would then be fair game for anybody to use.