@Frutis6, here an example with super professional textures:
To get this kind of setup, just get any kind of grid background and set it as texture in the MaptMaterial. Next, open up the MiniMapWidget and add two new images to the Overlay. Make sure the first one (in my example called viewport) is set as variable, the other can be left as default. In the first image, the one that is a variable, you set the image that will present the viewport, in the second image you set the cover that comes at the top and hides the corners.
Last step, disable map updates, this will prevent the grid from moving around and add a rotation to the viewport image so that it always point in the same direction which the player character is facing.
You can expand this further with only showing actors in front of the player character (though this would not be a real radar in my opinion) and make it nicer without the ugly cover, so on…
Hope this helps 