Download link for Big Sur continuously auto-shunts to Monterey link

You may be using older links that have been replaced since Monterey was released.

For Big Sur,

Open Safari and click on this link, 

How to get older versions of macOS

Go to the Use Safari to download macOS section and click on macOS Big Sur.

This will redirect you to the App Store Big Sur download page

it should say Get or Download. This will download the Install macOS Big Sur.app

to your Applications folder.

Before upgrading make a full back up of your Mac.

Check that third party apps you use have updates available for the new OS.

https://roaringapps.com

Check that your printers/ scanners etc have updated drivers and software available for the new OS.

Connect your mac to your router via cable rather than rely on WiFi.

Do not use your mac while it is downloading

and do not use any other devices that share the same internet connection.

If the App Store says ‘Open’ then it is detecting a previous download of the install app

go to the Applications folder locate Install macOS ******.app.

Move it to the Trash, empty the Trash.

Restart, click on the link again, the App Store should say ‘Get' or 'Download'.

If you are considering upgrading to Big Sur or Monterey be warned it does not support 32bit apps.

Your Mac is probably running 32bit apps and these will need to be updated to 64bit apps,

some updates may be free, some may be paid. Use this free app to discover which apps you have

are 32bit, https://www.stclairsoft.com/Go64/ then contact the developers of the software to see

if they are offering 64bit updates.

I have a 2017 iMac and tried to use the Safari link to install Big Sur, but when it opens the Big Sur link, I press the GET button, and it takes me to the Software Update within System Preferences. But after searching for Big Sur, I get the software not available message. Does it matter if I'm trying to upgrade from Mojave?

Tips How to Upgrade to Big Sur 

There are several points to consider before attempting the upgrade to Big Sur. The most important is Due Diligence on the part of the User and is a Prerequisite for a smooth upgrade.  

The below points should all be consider Before attempting the upgrade.

Point # 1 - Are there pre-existing Unresolved Software Issues. They should be resolved prior to upgrading - they may carryover to Big Sur making the system unstable / unusable.

Point # 2 - Are there any AntiVirus, Disk Cleaner, Optimizers, Un-installers, etc installed which should be removed as per Developers Instructions. They are useless, unneeded, cause havoc and interfere with the normal operation of the OS and may even Corrupt the OS requiring a Reinstallation. The The Built in Security  is all that is required.

Point # 2 A - Commercial VPNs should only be used if Mandated by Corporate Head Office for working remotely. Otherwise - ones Privacy and Security touted by the VPN is suspect.

Point # 3 - What are the How to get old versions of macOS  ie: Empty Space Requirements specific to the Big Sur. Apple states 35.6 GB Empty Space but suggest 50 GB

Point # 4 - Does the intended computer qualify for the upgrade.

Point # 5 - Are the installed Applications / Extensions compatible with Big Sur. Check with the Developer for compatible Apps / extension or do they offer updates. Same goes for Third Party Drivers for Printer, Scanners etc.

Point # 6 - If upgrading from Mojave and earlier versions of macOS - Remember that Big Sur does not support anything 32 bit. These include Applications, Extensions and Drivers for any devices. There is no workaround.

Point # 6A - To check for 32 bit Applications - a good application to use is Go64 - safe to use.

Point # 7 - Do I have a Rescue Plan In-Place. This comprises having 3 Backups using 2 methods and 1 Off Site incase of Theft, Loss or Natural Disasters. A Time Machine Backup  is very useful and can be used to Revert to Previous Working macOS. For addition purposes - two Tested Bootable Clones each to separate external drives. This is insurance incase the upgrades goes sideways. At least one Tested Clone and / or Time Machine Backup should be Off - Site

Point # 8  - To upgrade to Big Sur will requires a quick, stable and reliable Internet Connection - preferred method is via Ethernet Connection. 

If not available and using Wifi - move computer as close to the Access Point / Router and disconnect all other devices connected to Wifi. Want the maximum bandwidth for the computer being upgraded to Big Sur.