JoJo's Bizarre Adventure is teasing "important information" for the series in Summer. The third season of the anime covered the fourth part of the manga, Diamond Is Unbreakable. The most recent episode that aired was an OVA called Episode 5: Millionaire Village in 2017.
This new announcement could be a new OVA, Thus Spoke Kishibe Rohan: Mutsukabezaka or it could be that the anime is going to adapt Part 5 of the series, Vento Aureo.
A small plot of JoJo:
The series focuses around the mysterious adventures of the Joestar family, beginning with an encounter involving Jonathan Joestar, his adoptive brother Dio Brando and a mysterious Stone Mask.