Landscape is deleted in Play Mode

Good evening everyone

I have a problem. As soon as I go into Play Mode, the landscape deletes from the Outliner and is not rendered. Also in Editor, when I press G, the landscape is not visible anymore.
In the editor:

In playmode:

You see that Landscape is deleted from the Ouliner and is not rendered.

Where do I have to adjust that it is visible again?

Best regards and thank you in advance