I have a Ventura 27" iMac and I want to install High Sierra on an external SSD to run older programs but when I try from a bootable USB all I get is a no entry sign and if I double click on High Sierra in Applications I get "this copy of the Install Mac OS" application is too old to be opened on this version of Mac OS.
iMac 27″, macOS 13.3
FWIW, a 2019 iMac came shipped with macOS Mojave. Supposedly Boinx Fotomagico 5 ran on Mojave and possibly iDVD.
Which means, you could create a USB Bootable Installer of Mojave, possibly boot from it and install it to an external drive.
What year iMac? You can't run a version of macOS that is older than the version that shipped with your Mac.
macOS High Sierra 10.13 hardware requirements
The Age of this computer will Govern what version of macOS it will Qualifies to run.
Use About this Mac from the Apple Icon on Desktop - the required Information will be there.
Does this computer appear as Listed and Qualifying to run macOS 10.13 High Sierra ?
If Not, this computer maybe too New to run macOS 10.13 High Sierra even from an External Drive
Just to add, you may be able to run the app in question in a High Sierra virtual machine. Depends on the app.
IMHO and can be corrected by " others " - this machine is Too New to run macOS 10.13 High Sierra even from External Drive
You need a 2017 or earlier iMac to boot High Sierra.
FWIW, as I mentioned you can run a High Sierra virtual machine. However, without knowing what app you want to run it's not possible to say if it will run in a VM.
You're welcome. Just to add, there is no accelerated graphics available for macOS VMs, so if your apps require it, they won't work.
I have tried to install High Sierra on an external drive using a bootable USB. I tried using the option key at startup but when I selected the USB I got a '0' or no entry sign. When I tried double clicking it in Applications I got the message "This copy of the Install Mac OS is too old to be installed on this version of Mac OS".
The mac is late 2019 27" without the T2 chip.
You are welcome and thank you too for the opportunity to assist on this computer issue
Do come back to the Apple Support Communities ( ASC ) in the future if or when additional questions may arise.
Thanks for that, it looks like I may need a virtual machine. All I wanted was to put an older version on a SSD so I could run older software.
I want to run Boinx Fotomagico 5 as is is a bit glitchy in Ventura also if possible iDVD.
OK thanks for your help.
High Sierra
