Right, BSD is another minimalist option (technically not Linux, but superficially there are many similarities). There are multiple distributions of BSD to pick, derived from 2 main projects: FreeBSD and OpenBSD.

Downsides are similar to Gentoo, Alpine or Slackware: uber-minimal, so alot of skill & knowledge needed, and not always well documented to help you get there. Additional downside is hardware compatibility, you can't expect brand new (or even just very recent) computers (or peripherals) to work with BSD, the projects developing BSD distros don't have the same amount of resources to do the necessary work to get the same range of hardware working as exists for Linux.

Upside is that you'll be skillful and knowledgeable once you can handle BSD, and BSD is a secure choice