Surprise surprise! The sixth and final season of Lucifer will be released on September 10th, 2021. Leading up to the Comic Con @ Home Panel for Lucifer, the official twitter account for Lucifer @lucifernetflix played a game in which they’d release clues to a big s6 reveal. At the end of it all, it was a URL link that lead straight through to the s6 announcement trailer which you can find below that revealed the date.
Along with the announcement, Netflix also added Lucifer profile icons for your accounts of all the characters.

The panel was also uploaded on youtube in which Tom Ellis, Ildy Modrovich, and Joe Henderson talk about 5b and briefly s6 and what you can expect.
Lucifer seasons 1-5 are currently streaming on Netflix so you can catch up before the sixth and final season is released on September 10th.