Supergirl was renewed for a sixth and final season by The CW on January 7, 2020. Due to the coronavirus pandemic, the CW announced on May 14, 2020 that their regular season would start in January 2021 rather than October 2020 as usual. Along with this, they announced that Supergirl would return midseason. On September 22, 2020, it was announced that this would be the final season. It premiered on March 30, 2021.
SUPERGIRL is an action-adventure drama based on the DC character Kara Zor-El. Twelve-year-old Kara escaped the doomed planet Krypton and was sent to Earth where she was raised by a foster family. Kara grew up in the shadow of her foster sister, Alex, and learned to conceal the phenomenal powers she shares with her famous cousin, Superman, in order to keep her identity a secret. Years later, Kara was living in National City and still concealing her powers, when a plane crash threatened Alex's life and Kara took to the sky to save her. Now, Kara balances her work as a reporter for CatCo Worldwide Media with her work as Supergirl, keeping National City and the Earth safe from sinister threats. She's joined in this pursuit of justice by her sister, Alex, her mentor, Martian Manhunter and her friends Brainiac-5, Dreamer and Lena Luthor. As Kara struggles to navigate her relationships and her life as a reporter, her heart soars as she takes to the skies as Supergirl![src]
As Brainiac lays close to death after trying to stop Lex, Supergirl and team soar in to save him, engaging in an epic battle with Gamemnae. After beating Leviathan, Supergirl turns her attention to Lex who has used the Obsidian platform to brainwash half the world to love him and follow him at all costs, no matter what horrible things he does. Knowing how dangerous this makes her brother, Lena enlists the entire team – Alex, J'onn, Dreamer, Kelly and Brainiac – to help, but Supergirl realizes that the only way to truly stop Lex is to sacrifice herself.
As the stakes with Lex are raised higher than ever before, Lena must decide how far she is willing to go to stop her brother. Meanwhile, Supergirl and the team are faced with a challenge unlike anything they’ve ever dealt with before and it brings Alex to her breaking point.
Supergirl finds an opportunity to escape from the Phantom Zone, but it comes with some dangerous strings attached. Meanwhile, Lena joins the Superfriends on a mission but finds she disagrees with their plan of action against the Phantoms and wonders if she is truly ready to be a part of the team.
Nia and Brainy attempt to save Supergirl from the Phantom Zone by time traveling back to Kara's home in 2009. While determined to secure the item needed to help Supergirl, Brainy is worried about keeping a low profile so as not to alter the future timeline. However, when their ship crashes upon arrival, a young Kara Danvers is the first on the scene. Meanwhile, a young reporter named Cat Grant sets her sights on Midvale as she suspects there is a big story in the small town.
Part two of the flashback episodes pick up where things left off – Young Kara experiences kryptonite for the first time, Nia and Brainy are trapped by invading aliens, and a young Cat Grant may be the reason Supergirl never gets out of the Phantom Zone.
This season was rumored to begin filming mid-April to accommodate Melissa Benoist's pregnancy, but this plan was rendered obsolete once the COVID-19 shutdowns forced delays on all television productions. Filming resumed, tentatively, in September alongside the other Arrowverse shows.
Melissa stated in an interview that her maternity leave wouldn't be over until January.
However, before production could even begin, Supergirl had to shut down on September 30 due to delays in processing COVID-19 tests in British Columbia. Luckily, the stoppage was temporary.
On October 7, 2020, production was allowed to resume.