Flip-Switch seems to be missing under KDE settings (Task Switcher & Desktop Effects) unless it moved?
Some effects have been removed, and Flip-Switch is one of those, pending someone stepping in to re-write the code…
The only good thing about Vista!?!
At least “Flip-Switch” has a taker and is being worked on… 
Ie there a git page to follow progress?
Don’t know, sorry 
…
Most of the development for KDE is now hosted at https://invent.kde.org you could take a look around there.
Or, ask on the bug report I linked to, “Nate” (one of the KDE developers) normally responds, but it may take a few days…