Sierra 10.12.x is obsolete – No security updates since 2019. Most modern browsers and software no longer support it.
If you need it for a VM (VMware/VirtualBox) – you still must start with Apple’s official installer and convert it. No legal pre-built ISO exists.
Your ISO is not just for VMs. You can flash it to a USB drive to install Sierra on a bricked Mac.
Some older macOS versions remain downloadable via Apple’s support pages:
| If you want... | Use... | |----------------|---------| | Old software compatibility | macOS High Sierra 10.13.6 (same design, slightly newer) | | To run on old Mac | macOS Mojave (still gets security updates until 2025?) | | Lightweight virtual machine | macOS Catalina (min specs still generous) |