Preloaded macOS installer on bootable USB drive

Try the following:

#1 - boot into Safe Mode according to Start up your Mac in safe mode - Apple Support.

NOTE: Safe Mode boot can take up to 3-5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

#2 - go to the System/Software Update preference pane and begin the download.

#3 - run the installer from the Safe Mode.

I've had better luck from the Safe Mode because I evidently have some 3rd party software that interferes with the installation.

Only person with a Qualifying Apple Computer and having an Apple ID with Apple could do that. That is because, the Big Sur Full Installer must the downloaded from the Apple Apps Store.

Therefore - How to create a bootable installer for macOS is really the alternative.

1 - Connect to Router via Ethernet connection and restart the computer in Safe Mode and then open the Apple Apps Store and get the Full Installer of Big Sur. It will be the 11.6 version and once downloaded run the installer from the Applications folder.

3 - This method may seem unnecessary but sometimes the Router Restart clears Network issues from ISP to Apple Servers

Shutdown Router. Shutdown computer and disconnect all External Drives. Restart Router. Connect to Router via Ethernet Cable. If via Wifi - Disconnect all other Devices using the Wifi - want the Maximum Bandwidth only for this computer. Restart computer in  Safe Mode. It does a Repair Disk, Clear System Cache files and only load Apple Software, extensions and Fonts. Will load slowly - Normal. Once Logged in - open Apple Apps Store and  Get the Full Version of Big Sur. It will take some time and several pauses will occur - normal. Countdown clock may say 15 minutes but in Real time may be 30 minutes. Same goes for clock at 10 minutes could be 20 minutes in Real time. Eventually , Full Installer will download and a New Application in Applications Folder will present called Install Big Sur. Stop there and perform a Time Machine Backup. If desired - have an External Drive - Copy & Paste the Install Big Sur Application to external drive for future usage - making a Bootable Installer. Now run the Installer.

NYCPete wrote:

I've tried to download from the app store twice, and twice my my connection keeps getting lost. I simply cannot download from the Apple Apps store. What else can you offer?

Well with a Desktop computer you are bit stuck trying to move to a faster Network.

Option—

The Apple Store may help you if you take in a USB thumb drive to the store, give them a call an see if they will load it up with createinstallmedia.

When downloading from Apples servers it is always best to have your mac connected to your router via cable and not WiFi.

Do not use the mac while it is downloading or any other devices that share the same internet connection.

No. Apple only has them available via download.

Is this an UpGrade from previous version of macOS and if so what version ??

Or is this update to pre-existing version of Big Sur ??

That kind of information will help in offering a good assistance