With a near-fresh installation of NomadBSD (somewhat outdated FreeBSD 12.1-RELEASE-p6): pkg install bashtop – does not result in installation of python3. The subsequent run of bashtop reports: Error: Missing python3! (python37 is present, but not python3.)
Side note: I'm also aware of the https://github.com/aristocratos/bashtop/blob/9f8a1334933981ceb97f7daa90187e2f2fc70a13/README.md#L15 encouragement to use bpytop instead of bashtop. (bpytop does run without python3.)