How do i make a bootable installer of high sierra with ubuntu?

If your Mac has never had macOS 10.13+ installed, then you must find an original Apple SSD compatible with your exact model of laptop so that you can install macOS 10.13+ to the internal Apple SSD. There is no way around this requirement since the firmware updater found within the macOS 10.13+ installer requires a properly formatted & working internal Apple SSD. Keep in mind some other Macs may use a similar SSD with the same pin connector layout for the SSD, but they may not work in your 2015 MBPro since macOS can recognize the SSD is not compatible and may refuse to work at all. I have personally confirmed all of this with direct personal experience and experimentation.

If you already had macOS 10.13+ installed on this laptop, then in theory you should be able to boot into Internet Recovery Mode using Command + Option + R in order to install macOS 11.5 Big Sur. However, unfortunately some Macs will still default to booting the original OS which shipped with the laptop from the factory.

If you already had macOS 10.13+ installed on this Mac and Internet Recovery Mode is not booting to macOS 11.5 Big Sur, then you can in theory create a bootable macOS 10.13 recovery mode USB installer which mimics Recovery Mode, but you need to have access to the macOS 10.13 installer so that you can extract the necessary boot image which is possible using Linux. However, it is much easier if you have access to another Mac which is compatible with macOS 10.13 to 11.5 in order to create a bootable macOS USB installer using the instructions in this Apple article:

How to create a bootable installer for macOS - Apple Support

mrbobalina wrote:

I need to make a bootable installer of high sierra. I bought the OWC 2TB SSD Aura N2.

I'm running a dual boot with Ubuntu and my MacBook Pro 12,1. I went to go install my new SSD and my computer won’t even recognize there was a drive there. I read somewhere on the forum land that the firmware wasn't supported with an OS that new, and I need to run an OS as far back as high sierra. Maybe I'm off my rocker, I don't know. If anyone has a simpler way to get my computer back online with the new hard drive, I'd be stoked.

Thanks

Here is a link of the new SSD

https://eshop.macsales.com/shop/ssd/owc/macbook-pro-retina-display/2013-2014-2015

How to create a bootable installer for macOS - Apple Support

The older macOS installer backups on this server:

https://support.apple.com/en-gb/HT211683

verify you are using the Safari browser to download/initiate the macOS links.

I believe in High Sierra and higher, an SSD must be formatted APFS. Might check that with OWC.

These may help:

File system formats available in Disk Utility on Mac - Apple Support

Installing macOS on a separate APFS volume - Apple Support

I ran an APFS-formatted OWC SSD (2.5-inch form factor) in my Mid 2012 non-Retina MacBook Pro with High Sierra with zero issues.

I think what you want to do (with that MacBook Pro 12,1 late 2015) is attach an external drive, and install at least begin to install High Sierra 10.13.6, which should give you the firmware update in your Mac that supports nVME drives like your new SSD drive.

The firmware is (re-)written to a private store on the processor card, not on any drive.

You do not need Ubuntu to do this, you can use Internet recovery. That Mac was released with Yosemite 10.10, which you may need to install first to get access to 10.13.6 by selectively downloading exactly 10.13 version while running Yosemite.