When creating a bootable installer on these systems, you must append --applicationpath followed by the corresponding installer path to the command.

What is running on that machine right now? Share public link

💾 Always perform a Time Machine backup before attempting an OS downgrade or upgrade.

Select and follow the prompts targeting your freshly erased drive. Option B: Direct Upgrade (Keeps files intact) Select Install macOS directly from the main utilities menu.

A bootable USB drive is highly recommended for clean installations or troubleshooting multiple Macs. You will need a USB flash drive with at least 12 GB of storage, formatted as Mac OS Extended (Journaled).

If you already have a version of Sierra (10.12.x) and only need to reach 10.12.6, you can download the macOS Sierra 10.12.6 Update directly. 3. How to Install from a .DMG File macOS Sierra | Specs, reviews and EoL info - InvGate

This public link is valid for 7 days and shares a thread, including any personal information you added. This link or copies made by others cannot be deleted. If you share with third parties, their policies apply. Can’t copy the link right now. Try again later.

The internet is littered with fake DMG files and malware-ridden torrents claiming to be "macOS Sierra 10.12.6." Cybercriminals frequently inject ransomware into old OS installers.

The downloaded .dmg file is not the final application; it is an installation package container. You must extract it to create the actual application file.

Because macOS Sierra reached its formal End-of-Life cycle, its original cryptographic security certificates have expired. Launching the installer will often present a frustrating error message stating: "This copy of the Install macOS Sierra application is damaged and can’t be used to install macOS." All you need to know about MacOS Sierra - One2One Inc

To help narrow down the next steps for your installation project, please let me know: What is the Mac you are targeting?