Closing a window and closing an application aren't always the same thing.
I use Kubuntu 19.04, not Fedora, but I can use Alt+Q to close windows.
That setting is reflected in ~/.config/kglobalshortcutsrc
Window Close=Alt+F4\tAlt+Q,Alt+F4,Close Window
And Alt+Q works to close windows of Firefox, KInfoCenter, Konsole, Kwrite, and System Settings.
Operating System: Kubuntu 19.04
KDE Plasma Version: 5.15.5
KDE Frameworks Version: 5.57.0
Qt Version: 5.12.2
Is it possible you haven't installed KDE Plasma 5 completely?
I installed the KDE spin of Fedora from here in a VM to check whether Alt+Q works there to close windows. And it does.
Operating System: Fedora 30
KDE Plasma Version: 5.15.4
KDE Frameworks Version: 5.58.0
Qt Version: 5.12.1
Kernel Version: 5.0.17-300.fc30.x86_64
OS Type: 64-bit