Next step : mac mini in the garbage (seems to be no way to reinstall high-sierra)?

lanstrad1 wrote:

Changed the date in the system as I have access to Terminal in that setup, tried several, including a date before the last release of High-Sierra (October 2018). Same result.

High Sierra was released 25-Sep-2017 and EOL'd 12-Nov-2020. There were over 3 dozen builds between those dates. Since you probably don't know the exact build & date of the installer on your found USB key, try using a date in late 2017 in the hope that it will be earlier than the date of your installer.

Also, the High Sierra installer is still available here -> How to download and install macOS - Apple Support

The "servers" have not been closed "for older versions" as rumored throughout various forums. But they have not been consistently available for reasons we can only guess about and it's not necessarily Apple's doing. Just keep trying. I was recently able to download High Sierra, Catalina & Monterey by trying every few days. BTW, the downloads appear to work better using Safari than other browsers.

Also, the rumor that you can't create a bootable installer for an earlier version of macOS is false. I created two High Sierra bootable installers using my Catalina iMac. I think people mix up downloading macOS from the App Store with purely downloading via a browser; there is a difference.

I just successfully installed High Sierra on a 2010 and a 2011 MacBook Pro. I downloaded the High Sierra installer to the 2010, then followed steps from How to download and install macOS - Apple Support to make a bootable installer on an external SSD. I used Utilities to reformat the MBP hard drive, left utilities and installed from the installer. The only issue I saw was that I had to skip the iCloud install because it kept hanging up, then sign in later. The OS required one long update to be current. Good luck. It was worth the aggravation.

lanstrad1 wrote:

There is no way neither I could make a bootable USB with another mac as the ones I have here are newer and you need to use a mac that is working on High-Sierra!! We're stuck on all angles.

It doesn't need to be running High Sierra. I made my bootable installers for High Sierra, Catalina & Monterey on an iMac running Catalina.

I have an ongoing interest in High Sierra myself because I still have 3 Macs running it. There is some additional information about downloding the High Sierra installer on Mr. Macintosh. (Look for the website, I don't believe we may link it here.)

Start up from macOS Recovery

Option-⌘-R

Upgrade to the latest macOS compatible with your Mac.

In Disk Utility>View, select Show all Devices, highlight the top left entry.

APFS won't work for Sierra or earlier, Sierra or earlier needs MacOS Extended Journaled. High Sierra won't work for APFS on earlier Macs.

What has often worked for others is to use this Restore Method instead of CMD+r keys...

Option-⌘-R

Upgrade to the latest macOS compatible with your Mac.

could not create a reboot volume for apfs… - Apple Community

Remote Recovery Fails to install Sierra -… - Apple Community

Messed up Factory Reset on MacBook Pro Mi… - Apple Community

https://discussions.apple.com/thread/254793247?answerId=258936149022#258936149022

Clean Install of High Sierra: Multiple Fa… - Apple Community

An Error Occurred While Preparing The Ins… - Apple Community

Yes. You need to create a "bootable installer" — which you wrote you had already, but I am assuming you created it too long ago. As you wrote you need to do that on a Mac that can actually boot and run High Sierra. If I am not missing anything, it's the same solution MartinR described: you have to follow How to download and install macOS - Apple Support and have Safari redirect to the App Store.

I have been expecting Apple to obsolete even that method of installing HS, but as of a few days ago it still worked.

Forget the Recovery server method. That's been gone since May of last year.

Sorry, I'm out of ideas. :(

👍