sddm version 0.19.0 has been released more than two years ago: https://github.com/sddm/sddm/releases/tag/v0.19.0 Among other features it includes wayland support. We should upgrade.
There is no "wayland support" in 0.19.0, it still depends on X. Work is already under way towards a 0.20.0 release in the coming days, we won't look back. The state of its X-free Wayland display server support remains to be seen when that happens. *** This bug has been marked as a duplicate of bug 790713 ***