Mac Pro Firmware Upgrade Utility Released!

[ivr]

Figured it out. If you want to clean install Mac OS High Sierra, do not have the ethernet cable connected or wifi enabled! Otherwise you may get: "This copy of the Install macOS application is to old to be opened on this version of macOS."

Another crazy thing happened yesterday, I installed El Capitan than initiated HS upgrade from US within the OS. After installation completed it showed that Mojave was installed and not High Sierra. It looks like Apple is forcing installer to install Mojave instead of HS. Hope this helps someone.

[Bunga-Bunga]

Try setting manually date a few months/years back.

The problem is an expired certificate; you can't use older downloads after longer time.

[ivr]

Didn't need to set the date for High Sierra, I think that's for older Mac OS versions. For HS all I needed was to unplug the ethernet cable / disconnect wifi, otherwise installer forces Mojave. Strange and stupid, but it's true.