Hi, I want to install OS X Mountain Lion using Internet Recovery mode on my mid-2012 retina macBook Pro with its original hard drive, which has a working version of macOS Catalina. When I boot through Internet Recovery, I can't see my disk. Is there any way to install OS X Mountain Lion on my disk without wiping it?
MacBook Pro 15″, macOS 10.15
You can download Mountain Lion from here.Mac OS X Mountain Lion Installer You will need to make a usb flash drive thats bootable. As with Catalina installed ,you won't be able to install off the download.How to create a bootable installer for macOS - Apple Support You will need to partition your drive as Mountain Leon runs in Mac OS Extended Journaled.Partition a physical disk in Disk Utility on Mac - Apple Support
You can download Mountain Lion from here.Mac OS X Mountain Lion Installer You will need to make a usb flash drive thats bootable. As with Catalina installed ,you won't be able to install off the download.How to create a bootable installer for macOS - Apple Support You will need to partition your drive as Mountain Leon runs in Mac OS Extended Journaled.Partition a physical disk in Disk Utility on Mac - Apple Support
While booted from the Mountain Lion installer, you will need to partition & format the whole physical drive since older versions of macOS won't recognize the drive layout used by macOS 10.13+ which include Containers and the APFS file system. See this article on how to properly prepare a drive for a macOS clean install of 10.6 to 10.10:
https://www.owcdigital.com/assets/support/support-formatting-and-migration/Mac_Formatting_6-10.pdf
If you don't see the physical drive, then perhaps you are using a third party NVMe SSD in the Mac. If so, then you will only be able to install & use macOS 10.13+ since older versions of macOS don't have an NVMe driver. Use the instructions in @my ginger's post to create a bootable macOS 10.13+ USB installer.
Can't see my disk in Internet Recovery mode.
