/Applications/Install macOS Big Sur.app does not appear to be a valid OS installer application.

Thomas Decrick wrote:

trying to create an external installer using:

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

it always returns

/Applications/Install macOS Big Sur.app does not appear to be a valid OS installer application.

I've retried downloading latest Big Sur multiple times now on different computers running both Catalina and Big Sur. HT201372 does not appear to be helpful.

Hmmm...

I had no issues.. the installer has to be sitting in your Applications folder (the default location) as

"Install macOS Big Sur.app"

You can verify the path and name of your USB flash drive < /Volumes/MyVolume> Easiest to drag and drop it into the Terminal window.

Typically if you format the USB flashdrive it gets named Untitled. The createinstallmedia will name it appropriately when it completes the command... don't confuse the issue

So if you drag & drop to the window in will read /Volumes/Untitled.

There is a trailing space after --volume

sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume DRAG&DROP

Likely to do with the installer being 30mb large, and thus: empty. And no help that the process is opaque. The `createinstallmedia --downloadassets` does not illuminate much.

I'm having much saner results with this:

https://github.com/munki/macadmin-scripts

Yeps, seem to remember in some of the older macOS a similar issue where clicking on Get in the Apple Apps Store would only download the Stub 32 mb then had to run it to get the balance of the Full Version. Do not remember if in Apple Apps Store Control Click Get, or Right click Get or if clicking on Title of Big Sur another windows opened and would allow downloading the Full Installer. Get too old for this.

Likewise

MBP 2015 w. Mojave