Plasma Login Manager (PLM) will be the successor of SDDM for distributions using KDE Plasma.
However, some are clinging to SDDM due to it’s support of X11 features, which PLM does not fully provide. In recent months, there have also been some subtle changes in how SDDM is handled.
The following might be of interest for those who will eventually transition to PLM, but wish to hold on to SDDM as long as is practically possible: