Install Mojave on External Disk

The Apple " Licence of Use " probates installing or running a version older than what the computer Originally Came Installed with as New.

This will and does cover Installing on the computer or on an External Drive - period.

You can't run Mojave on a Mac that came with a newer version of macOS installed. If you have an M1 Mac, you can't even run it as a Virtual Machine.

As dialabrain says, not gonna work, sadly, except possibly...

How to create a bootable installer for macOS - Apple Support

How to Create a Bootable USB macOS Installer (2022) (onmac.net)

Yes, I read your question. If your Mac came with Catalina or later, Mojave will not run on your Mac. Not even if installed on an external drive.

Nancy, what year & Model Mac are you using to attempt this?

Nancy Blazis wrote:

2020 MacBook Pro

If you have an Intel MBP you could run Mojave as a VM in Parallels Desktop or VMWare Fusion.

If you have an M1 MBP, you can't.

BDAqua wrote:

As dialabrain says, not gonna work, sadly, except possibly...

A 2020 MacBook Pro shipped with Catalina. Mojave won't run.

I realize it won't run... forgot to check the 1st post as where it's mentioned where they want to run it, bit still can the USB Boot edition be used to install a VM?

Well as I mentioned above, if it's an Intel Mac a VM should work. Not on an M1 Mac.

Thanks.

Welcome.