Create a session switcher theme according to the mockup and these specifications:

v1 (if wallpaper can be transparent overlay) https://share.kde.org/index.php/
s/8oDkgG8Fg4JBobU
v2 (if not) https://share.kde.org/index.php/s/a55FSa7JyGxc885

The session switcher is as far as we can tell a rather strangely set up thing,
where all choices lead you directly to a lock screen to that active session,
as such the only options it display are active sessions and the ability to
start a new session, first leading to lockscreen for the sessions and the last
leading to SDDM. Like Lockscreen it is either a temporary, direct snap to
lockscreen/session switcher, or it has a smooth fade-to-black and a swift
fade-FROM-black to session switch.

The main difference between Session Switcher and Lock Screen is that instead of
having it cover the entire screen it is a black cover set at 70% opacity,
meaning you can see the entire desktop below. This since the Session Switcher
is not a security feature or privacy feature, it doesn't require the system to
hide anything from the user.

Critical: according to Dev feedback the background on Session Switcher will
use the lockscreen by default - so it will then use the opaque wallpaper set
by Lockscreen.