The same catalog you see in Cultiva → Settings → Plugins. Sandboxed extensions with sha256 integrity checks. Prefer Cultiva 2.0+ · Rowan. Cultiva 1.7 still works for many plugins but will soon stop being supported.
Install and enable plugins inside the Cultiva 2.0+ · Rowan desktop app (Settings → Plugins). Cultiva 1.7 still works for many plugins but will soon stop being supported.