Creating a bootable disk on a flash drive

Hello,

I have a 2011 27” IMac that I have installed a new hard drive and ram. I need to be able to create a bootable disk with High Sierra on a flash drive to install a new operating system on the new hard drive of the 2011 IMac. I am trying to accomplish this on my newer IMac that never had High Sierra installed on it and is currently running Monterey 12.1.

When I try to download High Sierra, the newer IMac gives a message that the system is up to date.

We have tried to download over WiFi using the tutorials has been unsuccessful. We have tried Tech support through Apple and OWC (maker of the installed hard drive) have been unsuccessful.

There must be a work around to accomplish this. Any help is appreciated.

Thanks Steve and Erin