How can I make a Dynamic wallpaper (like the ones in macOS Catalina) in OS X Yosemite
I don't think there is a way to do this effectively because dynamic wallpapers were introduced in macOS Mojave (10.14) alongside dark mode. The dynamic wallpaper is reliant on that although you could try doing an AppleScript script that changes the wallpaper based on the time or whether you're in dark mode or not. Wallpapers are found at the path /System/Library/Desktop Pictures. You can try adding your wallpaper(s) there and then using AppleScript or Bash as a startup item that is always running in the background and changed the wallpaper based on the time.