From the Live stream of Girls und Panzer das Finale in youtube its revealed that the third Girls und Panzer das Finale anime film is scheduled to open in Japan March 2021.
Rumor has it that Momo Kawashima, former student council member at Ooarai Girls Academy, is bound to repeat a year. Having failed her university entry exams, she is far from spending another year at Ooarai, but her plight is unenviable nevertheless.About the Anime -
The only way for her to gain admission into a university is to be granted an athletic scholarship. With the Winter Continuous Track Cup rapidly approaching, Momo becomes the commander of Ooarai's tankery team, so as to demonstrate her sport skills and wipe away the stain on her honor.
Their first opponent—French-themed BC Freedom High School—is split into two factions that are constantly at odds with each other. Despite this seemingly fortuitous match against a disorganized rival, Ooarai might soon find itself taking one step too far.
Girls und Panzer (ガールズ&パンツァー) is a Japanese anime franchise created by Actas which depicts a competition between girls' high schools practicing tank warfare as a sport. The series was directed by Tsutomu Mizushima, written by Reiko Yoshida and produced by Kiyoshi Sugiyama. Takaaki Suzuki, was involved in the production of the anime.
The TV series initially aired in Japan between 2012, with two additional episodes that aired in 2013 and an original video animation released in July 2014. Nine manga series and a light novel adaptation have been published till now.
An animated film was released in Japanese theaters on November 21, 2015. A six-part theatrical anime series has been announced, premiering from 2017 onwards.
Source - BANDAI NAMCO Arts Channel Youtube