Found a solution.
For anyone who is interested:
Use "Esc"-Button on full Keyboard für "Exit" and "Backspace" for "Back" (one step back in Menu).
But I have a new problem: how to bind "Teletext"?
The Back Command works as Exit.
If I press it, the whole menu closes.
I need the correct Back command to go one step back in the menu, not closing it.
Can anyone help?