Trying to create bootable macOS Catalina USB for late model 2012 iMac from 2020 MacBook Air

What dialabrain said.

You can only create USB installers with a Mac capable of using said installer.

To download Catalina for an installer you need an (intel) MacBookAir from 2012 to early 2020.

To download Sierra for an installer you need a MacBookAir from 2010 to 2017.

Your 2020 MBA is too new to download Sierra, and if it is the Late 2020 M1 then it is also too new to download Catalina.

You may need to find a friend with an Intel Mac to create an installer for you.

Do you have access to another Mac from 2007 to 2019? If so, then you can use that other Mac to download & create a bootable macOS USB installer using the instructions in the following Apple article:

Create a bootable installer for macOS - Apple Support

Generally you will need a Mac from:

• 2012 to 2019 (mid-2020) for macOS 10.15 Catalina
• Late-2009 to 2017 (mid-2018) for macOS 10.13 High Sierra
• 2007 to 2015 for macOS 10.11 El Capitan

The other Mac can currently be running any version of macOS 10.6+. You can confirm the other Mac is compatible with the OS using the information in the following article:

https://eshop.macsales.com/guides/Mac_OS_X_Compatibility

Unfortunately, even if you had a copy of the full Catalina installer, your new M-series Mac would not be able to create the bootable macOS Catalina USB installer (personal experience since I have some archived older installers). It is very unfortunate that Apple makes this so difficult.

Your other option would be to boot into Internet Recovery Mode using Command + Option + R to attempt to access the most recent compatible online macOS installer (should be Catalina). However, some Macs may only boot to the older online installer for the version of macOS which originally shipped with the Mac from the factory. Plus the hack the previous owner performed may affect how Internet Recovery Mode behaves on this iMac. I would suggest first performing a PRAM Reset (hold the keys for the PRAM Reset) for at least three chimes, then immediately hold the keys for Internet Recovery Mode before the computer has a chance to attempt booting into the internal drive. You can just hold the Option key, then once at the Apple boot picker menu you can press Command + Option + R.

It is very hard to download older macOS versions on newer macs. You can download the sierra dmg from here and see if you can open that

How to download and install macOS - Apple Support

make a bootable drive with that one and after you’ve installed that on the old machine, update to Catalina from there

Just to add, the page you were trying to download from are updates only. Not the full installers.

If you have an Intel 2020 MBA you can download the installer from here…

How to download and install macOS - Apple Support

If you have an M1 MBA, you can't.

One possible option, you can try installing macOS to the 2012 iMac from Recovery Mode.

How to reinstall macOS - Apple Support

Brock-M wrote:

Any ideas? Thank you for your help.

See my posts. Do you have an Apple silicon M1 MBA?

Last but not least, even if you could download Sierra, your Mac is to new to run the package in the Sierra DMG.

Now I'll take my leave.