Need to create High Sierra install DVD

The Sierra Installer I got is 5,233,568,296 bytes (5.23 GB on disk)

https://itunes.apple.com/us/app/macos-sierra/id1127487414?ls=1&mt=12

Early 10.11 Installer was 6,075,685,704 bytes (6.08 GB on disk)

https://support.apple.com/en-us/HT206886

https://itunes.apple.com/app/os-x-el-capitan/id1147835434?ls=1&mt=12

To get the full installer would likely be like this...

The High Sierra instructions...

http://osxdaily.com/2017/09/27/download-complete-macos-high-sierra-installer/

Of course I don't know if a DVD/DL will work or if it needs to be R&W media.

Some people seem to have missed a vital point from the original post. The post is saying Option for accessing the Boot Selection screen and Command-R for Internet recovery are not working. Hence it is not possible to use a standard USB boot drive.

One can presume that it may be the case that the Mac Pro has been fitted with an upgraded video card which does not have Mac firmware and hence does not support these pre-boot features.

A suggest for akadmon is to if possible fit the original video card which would have Mac compatible firmware and should support these pre-boot features.

A second suggestion would be to boot the Mac Pro in to Target Disk Mode by holding down T on the keyboard. Then connect it as an 'external' drive to another Mac. Then on this other Mac run the macOS installer or boot from a USB installer.

A third suggestion is to first make a USB boot drive - yes I am aware of the above issue. Then make a disk image of the USB drive, then convert the disk image to an ISO format. Then burn the ISO image to a dual layer DVD disc.

https://www.tweaking4all.com/cd-dvd-blu-ray-disc-burning/burning-for-macosx/convert-dmg-to-iso/

http://discoapp.com/

Like others have said I don't not know if producing a DVD this way will work. In theory a dual layer DVD should be big enough but it is unknown if it will work.

For burning an ISO to DVD try the one of the following, with no Mac having been built with a DVD drive for many years a lot of these programs are now quite dated.

https://simplyburns.sourceforge.io/

http://burn-osx.sourceforge.net/Pages/English/home.html

https://www.online-tech-tips.com/mac-os-x/burn-an-iso-file-using-mac-os-x/

https://discussions.apple.com/thread/8642432

http://discoapp.com/

I don't know about pre-sierra, but Sierra and on are on the support site. Just search for "Install macOS _____" in support.apple.com.

You used to be able to buy a Snow Leopard DVD on the Apple Store. I'm not sure that will work with your Mac Pro, though. The only version you could buy was 10.6.3, and I don't think that would boot a 2012 Mac Pro. It probably shipped with a later build of Snow Leopard.

Lion did not ship on a DVD, though you might be able to find a USB drive on eBay.

Internet Recovery doesn't work?

There are some articles on the internet that suggest ways to put it on a dual layer dvd, but some commenters said some methods didn't work.

Also, if it has not boot drive, it should attempt Internet Recovery without any keys.

You can create a bootable USB drive:

How to create a bootable installer for macOS - Apple Support

The installer won't fit on a DVD, so you're gonna have to figure out why the Option key doesn't work.

What happens when you press the Option key? Does the computer completely ignore it?

Do you have access to another Mac?

~Lyssa

Great suggestions John. :)