FreeBSD is a Unix-like operating system that has roots in Berkeley Software Distribution (BSD), which itself originated from research conducted at the University of California, Berkeley, in the 1970s.
The OS is known for its advanced networking features, security capabilities, and freedom-focused licensing, finding use in a wide range of hardware ranging from embedded systems to being the backbone of major cloud services.
Unfortunately, it looks like KDE’s Plasma Login Manager won’t be working on it, as an accepted merge request sees the focus turn to compatibility on Linux systems.
I mean, this is of course bad for people using BSD, but you can’t really fault devs for not supporting what you want. It’s FOSS. You support what you want, or you take what you get. Maybe support will come eventually, until then stick with SDDM or some other alternative.