This behaviour indicates that the keyboard layout is not set correctly. If a "+" appears when the button for "!" is pressed and the "@" sign does not work, the wrong layout (e.g. English instead of German) is probably active.

You can check and correct this:

°Windows:

- Go to Settings → Time & language → Language & keyboard.
- Make sure that German (Switzerland or Germany) - QWERTZ is active.
- Remove other layouts or switch with Alt + Shift or Windows + Spacebar.

macOS:

- System settings → Keyboard → Input sources.
- Select German and remove other layouts.

°Test:

- "@" should be on Alt Gr + Q (for German layout).
- "!" should be on Shift + 1.