@felinefowl You dont need any external applications in order to make META to work with Latte. You dont even need to use the Alt+F1 trick. You needs to happen is KWin to informed where to forward the META event.
To do that you can read at: https://github.com/psifidotos/Latte-Dock/wiki/F.A.Q.#q-can-i-use-my-super-key-to-open-the-app-launcher
The above is needed ONLY for the single META event. If you want to activate the rest META+… events of Latte you should go at
Plasma System Settings -> Shortcuts -> Global Shortcuts -> Latte Dock and activate them if they arent already (they can be deactivated if they are already used by another application)