Lack of artifacts

Hello.

There is a simple c ++ program that draws textured cubes. Using opengl (with related libraries).

The output is 2 layers of 12 cubes (each layer with its own texture). Layers are drawn in 2 consecutive draw calls (glDrawArrays ...), then glfwSwapBuffers and iterates.

Question:

Why is there no artifacts from overlapping renderings on the output frame?

Why do white glimmers appear on the edges?

Thanks