having trouble downloading latest version of Safari

The current version of Safari is installed with macOS. See the following:

The model year of an iMac is available at Apple menu > About This Mac.

A late-2009 through mid-2011 iMac can be upgraded to High Sierra 10.13.6 but no later version.

A late-2012 through late-2013 iMac can be upgraded to Catalina 10.15.7. See: https://support.apple.com/en-us/HT211683

A mid-2014 or later can be upgraded to the current version of Big Sur. See: https://support.apple.com/en-us/HT201475

To be specific, Safari is installed as part of the operating system and it normally it cannot be individually upgraded. It is periodically updated when the computer's operating system is updated or upgraded. If you can not upgrade your OS, you can use another browser that does work such as Firefox or Chrome. They can be individually updated as needed. Finally, even if you are able to update Safari, there is no guarantee that it will be compatible with every web site.