In Wayland, the compositor is the window server ( the equivalent of Xserver ). What you are looking for has to be a feature of the compositor and it is.
As others have said below, wlroots based compositors offer wlr-randr. There is also gnome-randr. For KDE, there is Kscreen-doctor. For X ( the window server being used by SDDM here ), there is xramdr.
Now, some people may see it as a problem that we have multiple Wayland implementations. I am mostly not fighting that battle. I will say that I hope these are not the same people that winge about systemd though and push for alternate init systems. I hope nobody that thinks MUSL is cool Is clinging to X11.
I would prefer that there was a common configuration standard for this stuff on Wayland. It will probably come eventually. Maybe as part of the freedesktop.org stuff.
Generally, I believe the Linux ecosystem has been stronger in areas where there has been competition between implementations ( even compilers ). I hope that Wayland will be one of those areas. As the core problems get fixed, the pace of innovation will increase. I believe we are already seeing that. There are more examples every day of things Wayland can do that X11 cannot. Let’s hope for more of that.