As a proof of concept I linked Factory/sddm to my home project home:giuschwim.
The changes consist mostly in configuration adjustments for Wayland, a Qt6 only
build and ripping out legacy code creating hard dependencies on xdm and
update-alternatives. For the sake of simplicity I removed the subpackages.
The build installs and works flawlessly on my laptop with a Slowroll Plasma
Wayland installation, also with an external monitor connected.

I am not a developer and my skills in writing spec files are very limited. This
could be a starting point for somebody with better skills.

Sddm-kalpa for Wayland in Factory is not intended for Tumbleweed/Slowroll. I
built it for Slowroll, but it was not installable with Plasma Wayland.