I too, thought lib32-systemd was a dependency of Steam, but this is not the case. See this GitHub issue.
https://github.com/ValveSoftware/steam-for-linux/issues/7355
There has been a new release of systemd, which is why the link isn’t working. I’ve been so busy uploading other packages, I haven’t updated the pkgver in the PKGBUILD. I figured if someone really wanted to use that package, they could easily update the pkgver to the latest systemd themselves. I’ll update it today.
Considering building packages is no fun for most people, I’ve just now made a package that downloads the required packages for Steam to run without the runtime for Obarun. It does download packages from a Artix repo, but it beats compiling them all yourself. You simply “pacman -U” the downloaded packages. Try it out and tell me how it works.
https://aur.archlinux.org/packages/steam-native-runtime-nosystemd/