Interesting thread, thought it was just me - the Super keys haven’t launched the menu for some time now (don’t know kow long. I didn’t notice until recently). I’ll try the suggestions in this thread & see if it fixes it.
N.B. I had the panels crash some time back; maybe this is something to do with it. I just replaced them.
What finally worked for me was this one terminal command from userbase.kde.org that stargazer linked to; Plasma/Tips - KDE UserBase Wiki
kwriteconfig5 --file ~/.config/kwinrc --group ModifierOnlyShortcuts --key Meta "org.kde.plasmashell,/PlasmaShell,org.kde.PlasmaShell,activateLauncherMenu" qdbus org.kde.KWin /KWin reconfigure
After I ran that command, it instantly started working again. Prior to this, no amount of rebinding to ALT+F1, or removing and re-adding the actual Launcher widget, would get it to work. And prior to that, I most certainly didn’t change any shortcuts. This problem started happening out of the blue as far as I could tell.
can you solve this problem???
Hi - I’m new to Manjaro and was experiencing this annoyance. I tried various fixes in this thread, but none of them worked for me. However, I think I’ve found out my issue. I’ve been switching between different themes since it’s a new install. I noticed that this is related to why my Meta key isn’t mapped to open the Application Launcher. Let me explain.
As I’m new to Manjaro, I don’t know the underlying theming mechanisms, but from what I understand is that you’re able to add numerous Application Launcher Widgets to a Panel. As such, each Application Launcher Widget is unique and has their own internal configuration, including keyboard shortcuts, which I assume this all boils up to a desktop layout configuration somewhere.
Now, by out of the box, Manjaro had mapped the Meta key to the ALW and in my case, that mapping mysteriously stopped working. My hypothesis for this is that as I changed themes and selected Use desktop layout from theme, the stock Manjaro configurations (including the mapped Meta key to ALW) was effectively overwritten. The culprit seems to be Use desktop layout from theme option. I’m not blaming that option, because that’s probably its expected behavior.
My solution:
Edit Panel
Configure → Keyboard Shortcuts
Meta (Windows) key (I had to use Meta-F1, since it requires 2+ key combination`)Meta key and test if it opens upFrom this point on, you’ll want to remember to not select Use desktop layout from theme or else your mapping will be gone when you switch themes, unless the theme provides that mapping by default (is that even possible?).
Yes, it’s annoying and it was fixed (and works with a new account).
However, before it was ‘fixed’ you could use ksuperkey.
The good news is - it still works.
pamac install ksuperkey
Reset the shortcut to Alt+F1
Set ksuperkey in autostart.
Log off.
The other way to manage it, and I use this for umenu which I’m testing this week, is to use Ctrl+z for menu…
Also remember Krunner - zero shortcuts for that if you’re on desktop (just type and it comes up). Sometimes I forget and open the menu - and wonder why I wasted all that time hitting the Meta key 
If any of you guys have Latte dock, don’t forget to check its settings, sometimes it’s the reason why you’re experiencing this issue with Meta key.
No, I set it there first. The truth is that even the main plasma panel has the same problem - not long after using a fresh desktop it lost the ability to open with Meta.
Yo guys i have found the solution,
I am using manjaro KDE Plasma latest 20.01 LTE
I had the same issue and I found the solution.
Here are the steps:
There is a lot of misinformation in this thread.
Shortcut Alt+F1 (works) selected Folder View…
Press Alt+F1 - get menu, press Meta - no menu.
Run ksuperkey - press Meta - menu pops up.
Thank you! It works for me.
Bro I have been trying to solve this for SOOO Long, and you legit saved me. You are a man of god 
Thanks a lot!
This one got my application menu to work with meta 
Doesn’t seem to work for me. And whenever it breaks seems to happen after using an application that’s trying to steal all keyboard input (remote sessions, virtual machines, etc).
Update:
Meta key fixed after reassigning launcher shortcut to Alt+F1. Now launcher is opening with both meta key and Alt+F1. Method:activateLauncherMenu in qdbusviewer is also working fine (I have undo changes in kwin config and have reconfigured it).
Worked for me, thanks!
I was using Latte dock, which worked fine with the meta key.
After I uninstalled Latte, I could not get Alt+F1 to work.
I ended up binding Meta+F1 and it only takes Meta to open the launcher.