iMac 2019 Unable to Upgrade Mac OS from Catalina v 0.15.7 to Big Sur v 11.6

I found the solution and the reason at this link: https://discussions.apple.com/thread/253139639, especially, "Here is my two cents, for what it is worth. I am guessing that the reason you are unable to successfully install your operating system is because the installer became corrupted during the download. The reason for this is because these are very large files and if you are using Wi-Fi, it often is too slow for these large files. Put the installer into the trash and do another download."

This gave me reason to attempt the upgrade to Big Sur 11.6 for the 5th time and it worked!

Unfortunately a search finds no Install macOS Big Sur.app in the Applications folder or elsewhere.

I do get a 2.9 MB 'Update' volume on my desktop, 2.8 MB of which is a restore log.

I have plenty, 992 GB of free space.

I do have backup.

This is the 3rd step in my effort do a clean install of my fusion drive iMac:

1. Using Command-R I received Catalina
2. I installed the Catalina upgrades that were offered.
3. When I select the Big Sur upgrade - see image below - I repeatedly end up with an incomplete download - see image above.

What options do I have left to get Big Sur?

Is this the Library structure you would expect to see in Disk Utility picture of Internal Drive that I'm attempting to upgrade from Catalina to Big Sur? I ask because there was no "Install macOS Big Sur.app" in the Applications folder that you had expected.

The upgrade attempts create a volume entitled "Update".