when I plug my external keyboard into my laptop the meta key just gets disabled. Meta+E or Meta+L do still work, but opening the start menu with just Meta doesn’t. It also disables this on the integrated keyboard. In the first second of the keyboard being plugged in it still works and then stops working for both. I also tested the external keyboard with another laptop running Windows and a desktop running Manjaro; on both of with Meta pulls up the start menu. Additionally, I tested another external keyboard, where the Meta key also works.
Keyboard making problems: https://www.amazon.de/EagleTec-Beleuchtete-Mechanische-Ergonomisch-Aluminium/dp/B07CMKJXG6
This could also be an issue with KDE like here because Alt+F1 still opens the laucher and suspending or rebooting while the keyboard is plugged in makes it work too.