Well, according to Variety, it turns out that for the film to pass censoring restrictions in India and the Middle East, a black dress was CGI'd onto Florence's body. Notice of the change was popularized on Monday by the fan Twitter account @bestofpugh.
A censored version of ‘OPPENHEIMER’ is being screen in several countries, with a CGI black dress covering Florence Pugh. pic.twitter.com/3SXea7pbCt
Since then, Variety reported that sources close to the film confirmed the censoring of the scene, as well as other sex scenes in the movie. Insider also reported the news, noting their sources associated with the film said that editing the movie for different countries is "usual business practice."