After entering a value for dimensions Blender shows zero I have a plane and when I enter a value in the Z dimension Blender shows me the value zero. Simply said I cannot enter a value in the Z dimension of this plane. But when I change the value of the Y dimension then in the viewport the Z dimension is changed. Anyone ?



As you can probably see the Z dimension of the plane is 10m but in the properties panel Blender says that the Y dimension is 10m
Dimensions are given in local view and your object is rotated around X. A way to see that is to activate the axis display option:



If you want to avoid that, the only way I know is what you stated in the comments: applying the rotation.