We have learned that Marvel Studios is currently searching to cast a Chinese-American woman between her 20s-40s under the code name of ‘Fang’. Although the description is brief, the character is described as being a secret agent.
Given it is for a feature film, the only two likely candidates that are currently in the stages of casting are ‘Doctor Strange: In The Mulitverse of Madness’ and ‘Shang-Chi’.
If the breakdown is for ‘Shang-Chi’, I personally think it could be for the character of Leiko Wu. For those who are unaware of who Leiko Wu is, she is a MI-6 agent who becomes romantically involved with Clive Reston, both characters are apart of the mythos of ‘Shang-Chi’ with Clive Reston already reported to be in the film, according to HN Entertainment. The code name of ‘Fang’ also could be a hint towards the iconic comic book villain Fin Fang Foom who has crossed paths with Shang Chi on multiple occasions.
As for ‘Doctor Strange: In The Multiverse Of Madness’, there is no specific characters I can think of who are part of the Doctor Strange mythos that would necessarily fit this description. Unless Scott Derrickson has decided to create a new character for the upcoming film which this agent could very well be.