How to add a blur behind a Popup activity

Question

I display a Popup based on an activity

MainActivity

btn_settings.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
        openPopup();
    }
});
    
private void openPopup() {
Intent popupwindow = new Intent(MainActivity.this, PopUpWindow.class);
    startActivity(popupwindow);
}

PopUpWindow

DisplayMetrics dm = new DisplayMetrics();
        getWindowManager().getDefaultDisplay().getMetrics(dm);
        
        int width = dm.widthPixels;
        int height = dm.heightPixels;
        
        getWindow().setLayout((int) (width*.9), (int) (height*.4));
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_BLUR_BEHIND, WindowManager.LayoutParams.FLAG_BLUR_BEHIND);
        getWindow().setBackgroundDrawableResource(R.drawable.bg_popup);
        
        WindowManager.LayoutParams params = getWindow().getAttributes();
        params.gravity = Gravity.CENTER;
        params.x = 0;
        params.y = 0;
        
        getWindow().setAttributes(params);

To give you an idea the width*.9 must display a left and right margin of ~10dp and height*.9 must display 1/4 of the height of the phone

Behind the Popup you can see my MainActivity, I would like to know how to add a Blur around my popup

I also thought of a black background with ~80% transparency

If you have the solution for both it would be very appreciated but one will already be really great!!

Thanks you