I asked GPT why:

In the early 1990s, Prince was embroiled in a contractual dispute with Warner Bros., his record company. He felt they were restraining his creativity by not allowing him to release albums as frequently as he desired. In 1993, in an act of rebellion, he changed his name to an unpronounceable symbol, which was a combination of the male and female gender symbols, in order to free himself from his contract obligations to Warner Bros. Since the symbol had no pronunciation, he was often referred to as "The Artist Formerly Known as Prince" during that period. He returned to using the name Prince in 2000, after his publishing contract with Warner Bros. expired.