why is my system preference window not showing that I need to upgrade (from BigSur) to Monterey?

You would need an iMac introduced in Late-2015 or later to receive an upgrade message in Software Update for Monterey. You can confirm this in the Apple () menu > About This Mac panel. See the product description line on that panel.

mary alice from florida wrote:

I have auto updates checked. I did have a red indicator on my system pref icon but that is not there either.

i have seen here before that when auto updates are enabled, for some users checking manually for updates fail. i would first disable auto updates, restart your mac, and then try to manually upgrade again.

mary alice from florida wrote:

why is my system preference window not showing that I need to upgrade (from BigSur) to Monterey?

You can initiate the download from the App Store

verify you initiate the link with Safari browser

See #3—How to upgrade to macOS Monterey

How to upgrade to macOS Monterey - Apple Support