OK NO 4TH SEASSON FOR NOW BUT JUST 3 MOVIES WERE ANNOUNCED

2021 will have 2 "Episode of Roselia"

1st one: "Yakusoku"

2nd one: "Song I Am "

These will likely cover the Future World Fes Arc

And in 2022 will have "Poppin'Dream", focus on Poppin' Party

Source in English: https://twitter.com/bandori_updates/status/1253326503724503040?s=19

Japanese source: https://twitter.com/bang_dream_info/status/1253331182344744961?s=19