Yeah it looks like they dropped it in 2021 and AFAIK there isn’t a replacement yet. Unless anyone here knows of one, which would be gratefully received!

(Relevant part from link):

The latest Plasma release dropped a few desktop effects: the cube family, CoverSwitch and FlipSwitch. All of those effects were written back in 2008, the early days of KDE 4.x and the early days of desktop effects in KWin. The effects were implemented by me and when Vlad asked about removing them I saw the need for this and supported this step for technical reasons.