I use nix on both mac and linux, also on CI where homebrew is especially brittle
From that:
- create a new APFS volume for your Nix store
- update /etc/synthetic.conf to direct macOS to create a "synthetic" empty root directory to mount your volume - specify mount options for the volume in /etc/fstab: rw: read-write, noauto: prevent the system from auto-mounting the volume (so the LaunchDaemon mentioned below can control mounting it, and to avoid masking problems with that mounting service), nobrowse: prevent the Nix Store volume from showing up on your desktop; also keeps Spotlight from spending resources to index this volume
- if you have FileVault enabled: generate an encryption password, put it in your system Keychain, use it to encrypt the volume
- create a system LaunchDaemon to mount this volume early enough in the boot process to avoid problems loading or restoring any programs that need access to your Nix store
Even as someone who knows how to do all that... no thanks.