A Texture2DArray is different from a Texture3D: The Texture2DArray does not support trilinear interpolation between the Images, i.e. no blending. See also Cubemap and CubemapArray, which are texture arrays with specialized cubemap functions.

A Texture2DArray is also different from an AtlasTexture: In a Texture2DArray, all images are treated separately. In an atlas, the regions (i.e. the single images) can be of different sizes. Furthermore, you usually need to add a padding around the regions, to prevent accidental UV mapping to more than one region. The same goes for mipmapping: Mipmap chains are handled separately for each layer. In an atlas, the slicing has to be done manually in the fragment shader.

To create such a texture file yourself, reimport your image files using the Godot Editor import presets.