On my Mac, I just use whatever the default static wallpaper is. Or I pick one of theirs. I always have widgets covering my wallpaper and I don't know how to easily see what it is (short of → Settings → Wallpaper), but I think it's like a forest/hills. On my MacBook it's a lake.
On my phone, I have a Star Trek theme. LCARS (the OS on Next Generation) lock screen, and one of the ships (I think it's Discovery, I never really look that closely at it) warping up toward the top with the trails down between the icons.
I mostly don't care what the wallpaper is because I never look at it, but I'm too proud to just have it black (nothing there). I know that's an option on Windows (no wallpaper, and there's a setting for the desktop colour), but I'm not sure about Mac or iOS.
I almost envy people who have "cool" wallpapers (my wife has a bunch) but I mostly can't be arsed. Like... I wouldn't mind having digital frames with rotating wallpapers or fan art or whatever. But my desktop? It's a workspace and I have work (or "work") covering it all the time.
Meanwhile, their biggest competitor is either Linux or UNIX. That is, if you accept that macOS "is UNIX." It's been UNIX certified for a couple years now, but it's UNIX in name only. While Steve Jobs' NeXTStep was based on UNIX, NeXTStep was also vapourware. Still, it became OS X which became the macOS we know and love (or hate) today. But the truth is, it's UNIX 3 certified, which is a decades-old certification, and it only just barely makes that. So it's a thing Mac users brag about. "A UNIX system! I know this!" Jurassic Park meme. And then of course there's Linux. And of course Windows has the Linux subsystem. Still, non-*nix is going the way of the dodo, just like Win9x did when Microsoft realised WinNT was the future. First with the tranwreck that was WinME, but much more importantly with WinXP. And NT was good, but its time is up (or will be soon).