There has been no official announcement for the next TV anime series that should follow the ongoing Aikatsu on Parade! so far.
Based on Bandai’s game series of the same name, the first Aikatsu! TV anime was aired for 178 episodes from October 2012 to March 2016, then followed by the second series Aikatsu Stars! with 100 episodes from April 2016 to March 2018 and the third series Aikatsu Friends! with 76 episodes from April 2018 to September 2019.
The latest fourth series Aikatsu on Parade!, a crossover series featuring all idols from the past installments, has been aired in Japan since October 2019.