summary: Everything looks/works fine with scaleSize 2, but doesn't with 1.

(NOTE: Also, the collision doesn't work when the scaleSize is 1, although scaleSize has nothing to do with the collision process (only the size of the collision boxes, but they are drawn so I see that there's nothing wrong with them), that's another question so I will post this as a separate one.)

example:

summary: Everything looks/works fine with scaleSize 2, but doesn't with 1. -> edit: scaling doesn't work well.

public void LoadContent()
{
    Graphics.PreferredBackBufferWidth = 1920;
    Graphics.PreferredBackBufferHeight = 1080;

    currentWidth = GraphicsDevice.Viewport.Width;
    currentHeight = GraphicsDevice.Viewport.Height;

    preferredWidth = 800;
    preferredHeight = 450;

    scaleWidth = currentWidth / preferredWidth;
    scaleHeight = currentHeight / preferredHeight;

    scale = Matrix.CreateScale(scaleWidth, scaleHeight, 1.0f);

    this.Graphics.IsFullScreen = false;

    Graphics.ApplyChanges();
}

int currentWidth;
int currentHeight;
int preferredWidth;
int preferredHeight;
float scaleWidth;
float scaleHeight;

public Matrix scale;
GameWindow Window;
ContentManager Content;
GraphicsDeviceManager Graphics;
GraphicsDevice GraphicsDevice;

public ScreenSize(GraphicsDevice graphicsDevice, GraphicsDeviceManager graphics, ContentManager content, GameWindow window)
{
    Window = window;
    Content = content;
    Graphics = graphics;
    GraphicsDevice = graphicsDevice;
    LoadContent();
}

public void LoadContent()
{
    Graphics.PreferredBackBufferWidth = 1920;
    Graphics.PreferredBackBufferHeight = 1080;

    currentWidth = GraphicsDevice.Viewport.Width;
    currentHeight = GraphicsDevice.Viewport.Height;

    preferredWidth = 800;
    preferredHeight = 450;

    scaleWidth = currentWidth / preferredWidth;
    scaleHeight = currentHeight / preferredHeight;

    scale = Matrix.CreateScale(scaleWidth, scaleHeight, 1.0f);

    this.Graphics.IsFullScreen = false;

    Graphics.ApplyChanges();
}