Turned out I had modified the file ~/.config/kwinrc when I installed Latte
dock and after I removed it, the meta key was no longer activating Plasma's
application launcher.
To enable it again open ~/.config/kwinrc and update the following section:
kwriteconfig5 --file kwinrc --group ModifierOnlyShortcuts --key Meta ""
(it writes a config key in ~/.config/kwinrc that should prevent the meta key
from opening the launcher...you may need to re-login into plasma for this to
take effect. )
Below is the original answer relating to the default behavior in 18.04.
As discussed in an older question,
if you have mapped it to something else,
setting the shortcut key to Alt-F1
automatically enables the super key
as a shortcut to open the application launcher.
Here it is for kickoff (a.k.a. Application Launcher):
and here it is for kicker (a.k.a. Application Menu):
I have verified that this works for both on my machine running 18.04. It looks like you are using kicker, so you should be able to enable this behavior on your machine.
This feature was announced at the time:
Thanks to our Wayland effort, we can finally offer so-called “modifier-only
shortcuts”, enabling you to open the application menu by just pressing the
Meta key. Due to popular demand, this feature also got backported to the X11
session.
Today I’m happy to announce that for the first time we were able to backport
a new feature from our Wayland offerings to X11: modifier only shortcut
support. This is one of the most often requested features in Plasma and I’m
very happy that we finally have an implementation for it.
Modifier only shortcuts mean that an action is triggered if one clicks a
modifier key without any other key. By default the Meta (also known as super
and windows) key triggers the main application launcher of your Plasma
session. But the implementation is way more flexible and allows to use any
modifier (ctrl, alt or shift) as a trigger for an action (currently
configuration is only possible through manual modification of kwinrc).
Add a dbus call to activate the "main" application launcher
ShellCorona provides a new DBus method "activateLauncherMenu". If that is
invoked it will look through all panels for an applet which has
X-Plasma-Provides with org.kde.plasma.launchermenu. If that also has a global
shortuct it gets activated and no further applet is searched.
The idea behind this DBus call is to provide a way to KWin to activate the
main appliction launcher when the Meta key is pressed.
Edit: After some help from @DKBose I am 90% sure this is a duplicate of an older question:
How to activate application launcher using meta key
Relevant excerpts:
and from the linked forum post:
Below is the original answer relating to the default behavior in 18.04.
End of edit.
Plasma 5.8 and later exhibits this behavior by default. If you have Plasma 5.8 or later installed and the Super/Meta/Windows key does not open the application launcher, this is because of an old configuration file.
As discussed in an older question, if you have mapped it to something else, setting the shortcut key to
Alt-F1
automatically enables the super key as a shortcut to open the application launcher. Here it is for kickoff (a.k.a. Application Launcher):and here it is for kicker (a.k.a. Application Menu):
I have verified that this works for both on my machine running 18.04. It looks like you are using kicker, so you should be able to enable this behavior on your machine.
This feature was announced at the time:
https://kde.org/announcements/plasma-5.8.0.php
https://blog.martin-graesslin.com/blog/2016/08/modifier-only-shortcuts-available-in-plasma-5-8/
Here are the commits in August 2016 that added this:
https://phabricator.kde.org/D2357
https://github.com/KDE/kwin/commit/9b30cfef1d212ed2b40510a70d1f92c497f44398
https://phabricator.kde.org/D2356
https://github.com/KDE/plasma-workspace/commit/267b6a8dfb4ad3b4f9da010d2aeaeebec25c5c0f
Related:
In KDE 5.18 set Meta+F1 as shortcut (Meta key means Windows key)
after it work on just meta keypress