I have installed KDE Plasma 5.9 on my Arch Linux and I deleted the application launcher and then made a new panel with adding the 'application dashboard menu' launcher widget that is full screen. I then assigned it the key Alt + F1 global alternative key and after running the ksuperkey, it just worked only when pressing the meta key for a second not just directly pressing it.
I guess pressing the meta key requires another key to complete its act as a modifier but due to ksuperkey, I think it just waits for a sec for another key combination and if it doesn't happen in a second, the super key acts standalone.
Please correct me and tell me how to use the meta key without any delay without disturbing other key combinations with the meta key if I need.

Hey, author of ksuperkey here. First of all, as noted in the README, you don't really need ksuperkey in Plasma 5.8 and above - this functionality is now included by default. Secondly, ksuperkey will trigger the key event when you release the key. When you hold down the key, it'll work as a modifier, but if you press and release the key without pressing any other keys, ksuperkey will interpret it as a normal key press.

So in short: try to press and release the key quickly. There could also be a conflict with the built-in functionality that creates the delay, so you can also try to deactivate ksuperkey and see if it works.

Thank you so much. Deactivating ksuperkey worked!