sudo: /Applications/Install OS X El Capitan.app/Contents/Resources/createinstallmedia: command not found

Your 2019 iMac is not compatible with the El Capitan OS needed to create the bootable installer.

You'll need to look at the options 1) or 2) that den.thed posted, or find an older Mac (late-2015 or older) that is compatible with El Capitan and use that to create your bootable installer.

Please see: Create a bootable installer for macOS - Apple Support

1) Use the original gray Disc set that came with the 2007 iMac.

2) Use a Retail Leopard Upgrade DVD, a Retail Snow Leopard Upgrade DVD or the Retail Lion Upgrade on a Flash Drive.

3) Create an El Capitan bootable installer

Create a bootable installer for macOS - Apple Support

Well, you would need a copy of the El Capitan installer from How to download macOS but I expect your current Mac may be too new to create one. You could try it.

Which install disks do you have?

FWIW, a 2007 iMac has zero value and even if you could get El Capitan installed on it, it's no longer supported, won't run any modern software or be able to access many websites etc. If it were mine, I would take it to the nearest Apple Store to be recycled.

DamonJynx wrote:

1. I don't have it. I do however have ti=he install discs from a Macbook of the same era but it doesn't load.

2. Don't have.

3. This is what I've done, but following the instructions results in the: command not found message.

1. Disc's from other Mac's are system specific will not work.
2. Apple no longer sells the Retail Upgrades, but you can still find them at Amazon and E-Bay.
3. You need to use an older Mac, but that hinges on connecting with the server and other obstacles.

Assuming you've already downloaded El Capitan, the correct Terminal command is…

sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app

You have to either name the USB flash drive you are using to MyVolume or change MyVolume in the command to the name of the flash drive.

DamonJynx wrote:

Looks like a trip to the local Genius Bar, hopefully they have old discs that will work...

FWIW, Apple does not keep install disks around. About the only place you can find them is on ebay.

Once you find a Mac that's suitable for creating your bootable installer …

Please make sure that when you enter the command, you type a backslash (\) character before each embedded space in the file name. If you don't do this, the shell will interpret the spaces as separating different parameters, rather than as being part of the file name. Then you'll get a command not found error because there wasn't any command called /Applications/Install.

sudo: /Applications/Install OS X El Capitan.app/Contents/Resources/createinstallmedia: command not found

Good luck. 🍀🙂