It's difficult to say whether or not this drama is a publicity stunt. This Forbes article details the drama between the two celebrities. Considering that Selena Gomez's follower count went up considerably, and her businesses gained an increase in attention, it could be a publicity stunt designed to get more attention for Selena. However, I doubt a publicity stunt would go that far considering the damage it did to Bieber's reputation and the death threats she got. It appears that the drama was perpetuated by TikTok users, who made many accusations and conclusions based on a few things that were posted on social media. I seriously doubt this was a publicity stunt for that reason, rather, just another trend on TikTok to keep people entertained. However, it cannot be determined for certain if it was a publicity stunt or not.
https://www.forbes.com/sites/conormurray/2023/03/28/is-the-selena-gomez-and-hailey-bieber-social-media-drama-over-the-whole-controversy-explained/?sh=51f061c55a37