Is it possible to somehow disable the showing of backdrop/background images for movies, and instead show a default image, the same way as it is possible in the "Wallpaper" setting for Poster Wall background?
No, there isn't a setting to do that. There is a workaround though - create fanart jpgs of your desired background and put them into each movie folder named like movieName-fanart.jpg and switch on local images. Bit long winded but it'd be possible to write a batch file to do it.
Then you have to continue reading. On lines 8–10 I’m defining the properties of the h1 element inside the header, specifically a transparent background and text color to override the busy and noisy background image. This is what it will look like in action:
