Restart Gnome 3 Shell without logging out and without loosing running applications.

press Alt + F2, type "r" then Enter. This will work so long the shell isn't unusable.

if Shell is unusable then try

Ctrl +Alt + F1 to take you into a shell

and then send SIGQUIT to the gnome-shell process which will terminate only the shell:

killall -3 gnome-shell

Restart KDE Plasma windows environment without logging out

Alt f2
then type
killall plasmashell

Alt f2
then type
kstart plasmashell