Expired certificate. Apple’s signing certificate for High Sierra expired in October 2019. Solution: Open Terminal and set the system date back to when the certificate was valid:
Unmount the volume and move the finalized .dmg file to your desktop for easy access. How to Create a Bootable USB Drive Using the DMG
Here’s a blog post designed to help users safely find and install macOS High Sierra 10.13.6. macos high sierra 10136 dmg
The final update — 10.13.6 — includes security patches, stability improvements, and support for AirPlay 2 multi‑room audio in iTunes, along with enhancements to Photos and Mail.
To perform a clean installation or fix a crashed Mac, convert your file into a bootable USB drive. You will need a USB flash drive with at least 16GB of storage capacity. Note that this process completely erases the flash drive. Plug your USB flash drive into the Mac. Expired certificate
(Build 17G65) is the final major update for the High Sierra operating system, released by Apple on July 9, 2018. While officially superseded by macOS Mojave, it remains a critical "bridge" OS for older hardware and users needing specific features like AirPlay 2. Core Technical Profile Latest Version:
Essential for clean installations on Macs that cannot connect to the internet. How to Create a Bootable USB Drive Using
High Sierra SSDs and Fusion Drives to APFS automatically. HDDs remain HFS+ unless you manually convert. Don’t fight it – APFS is more reliable for SSDs.
Better recognition for HEIF and HEVC media formats.
The following Macs are compatible with High Sierra: