MarsSeed [1] filed a deletion request for steamos-compositor [2]: SteamOS Compositor has been abandoned since 2019 [a], in favor of Valve's successor fork, gamescope [b]. The latter is available in Arch repo. [c]
[a]: https://github.com/ValveSoftware/steamos-compositor [b]: https://github.com/ValveSoftware/gamescope [c]: https://archlinux.org/packages/?q=gamescope [1] https://aur.archlinux.org/account/MarsSeed/ [2] https://aur.archlinux.org/pkgbase/steamos-compositor/
