A popular niche includes small, "chibi" style robots or robots in unexpected natural settings, like holding a flower or wandering through a forest.
For reliable downloads without low-resolution issues, these sites are highly recommended: 1920x1080 Robot Wallpapers | Best Wallpapers
Zedge offers a massive library of user-uploaded content with a specific category for robot backgrounds. A popular niche includes small, "chibi" style robots
WallpaperSafari and WallpaperCave are excellent for curated collections of "best" and trending images. A popular niche includes small