Wait a minute… Do you have the ca-certificates package installed? Or maybe that’s stored in a different location on your system… You’re on a BSD right?
Edit: Well I’m going to guess that since you’re on FreeBSD, the smallstep trust install command doesn’t know what to do which is why we see “trust not supported”. I’ll need to dig into that to find out when they message is written.
From a bit of Googling, looks like FreeBSD now uses Mozilla’s trust store (aka NSS) as the system trust. This seems to be shipped as a single file that apps are meant to read from. Idk what to suggest, cause I’m not a BSD user.