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[pastrychef]

Well I created 2 partitions on 32GB Thumb drive and created install media for Catalina and Big Sur then put my OC EFI folder on the EFI partition. I restarted, cleared NVRAM and did F12 to select it to boot from. I know the EFI is working because I used OC 0.6.9 and not 070beta which is on my main boot drive. Unfortunately, in the boot menu the installers do not show up.

View attachment 519925

You mean the BIOS boot menu doesn't see your USB flash drive as a boot option?

 

[Edhawk]

So you Formatted/Erased the USB drive in Disk Utility as shown below:



When the Erase operation was completed, you had a USB drive with a single partition visible named 'Untitled'.


You then Partitioned the USB drive so it had a second partition visible, named 'Untitled 2'


Your USB looked similar to the one shown below, i.e. two partitions visible and a hidden EFI partition.


I personally removed the space in the name 'Untitled 2' so the partition was named 'Untitled2'. This just kept the createinstallmedia command for Big Sur more straightforward.

You then used the following Terminal Commands to install Catalina and then Big Sur on the two partitions.

Catalina - sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled

The 'Untitled' icon was renamed 'Install macOS Catalina' on your desktop.

Big Sur - sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled2

The 'Untitled2' icon was renamed 'Install macOS Big Sur' on your desktop.

renamed icons for macOS Catalina and Big Sur.

Each time the 'CreateInstallMedia' process was successfully completed and the USB was set as bootable, yes?

With a Terminal screen similar to this visible after the Catalina installation process completed.



And a Terminal screen similar to this visible after the Big Sur installation process completed.



You then mounted the EFI partition on the USB, using Hackintool or a Terminal command.
Copied your working OpenCore EFI folder to the root of the EFI partition on the USB.
Booted the system with the USB plugged in to a functioning USB port.
Pressed the F12 key to bring up the Gigabyte Boot Menu, where you selected the UEFI partition on your USB drive.
OpenCore booted to the Picker List or GUI and the two installation icons were not present.

They should be if you followed these steps set out above.

Are you going to try again?

 

[Edhawk]

I just went through the steps outlined above, using a 64 GB USB drive to add the two installers. The two installer icons appear on the OpenCore GUI boot screen, as highlighted in the red rectangle on the screenshot below.



OpenCore 0.6.9 GUI with two installers visible and available to boot.

 

[JBX]

Interesting Edhawk... I will try again (although I did just what you described above).

 

[Edhawk]

Check the settings you are using when you Erase the USB, i.e. Guid Partition Map selected as the Scheme and not Master Boot Record. It is the most obvious place for a issue to arise, that would enable you to install the two OS's but not be able to boot either.

 

[JBX]

It is GUID Partition Map. And each partition is Mac OS Extended (Journaled).

Second try failed to show installers. I recently updated my motherboard bios... so I checked if I had missed something by trying my Catalina 10.15.5 installer and that one works fine.

 

[pastrychef]

It is GUID Partition Map. And each Mac OS Extended (Journaled).

Second try failed to show installers. I recently updated my motherboard bios... so I checked if I had missed something by trying my Catalina 10.15.5 installer and that one works fine.

If BIOS is not seeing your USB flash drive as bootable option, something might be wrong with your EFI.

 

[JBX]

I found the problem. On my motherboard for a bootable Catalina installer I must use iMac19,1 SMBIOS. I have been using iMac20,1 which works with Big Sur installer, Big Sur and Catalina once they are already installed on a disk.

I don't know why then it would not just show the Big Sur installer in the boot list. Maybe because Catalina install media was created first.

 

[pastrychef]

I found the problem. On my motherboard for a bootable Catalina installer I must use iMac19,1 SMBIOS. I have been using iMac20,1 which works with Big Sur installer, Big Sur and Catalina once they are already installed on a disk.

I don't know why then it would not just show the Big Sur installer in the boot list. Maybe because Catalina install media was created first.

I don't know why iMac20,1 gives you problems. If iMac19,1 works, why not use that? Both iMac19,1 and iMac20,1 should work with Big Sur. Sounds like you may have some configuration issues.

 

[JBX]

Yes, I don't know why. My config has been very much the same since last summer when I built this system that with only the changes in each newer version of OpenCore release adhered to the OC guide. But I have never been successful in booting a Catalina Installer Media with iMac20,1. I have had to use 19,1 just to get it installed on disk.

I just did more testing with using my current EFI OC 070b and my previous OC 069. They both boot but fail to show the installers when they are on the same thumb drive. I can see the installers using a copy EFI from another installer containing OC 063 / Catalina Installer. I will go back to individual installer thumb drives and test my EFI's again as I did last have the same copy of OC 069 booting Big Sur installer. Will update this later.

Update:
Well my issue is definitely with my config of OC 069/070b. I re-created just a Big Sur installer thumb drive and I could not see the installer with those two. I had to use my older copy of OC 068. Will have to spend some time on it later but it is interesting that once an OS or multi OS's are installed it all works fine.

Update 2: I fixed my OC 069 and 070beta EFI's they work fine now and show the installers (just the SMBIOS needs to be swapped out for 19.1 for Catalina installer).

But anyway, the method of having multiple installers on a single disk dose work. Thanks everyone and back to the original subject... I need to buy more thumb drives.