I make it short, this is what I'm aiming for:
and in Godot:
Not very square, I solved this in Blender by changing the aspect ratio, which is not quite desirable in a game. A working option in Godot would be to scale the depth and the height by a multitude of 1,414 or √2 but I don't know, I'm lazy and don't want change scale for every object, can it be done via shader? I searched for aspect ratio and scaling shaders but no result so far. Or maybe someone has a more elegant way to solve this?