To update Safari from 13.0.5 you would need to upgrade the macOS on your iMac.
The model year of an iMac is available at Apple menu > About This Mac.
A late 2012 through late 2013 iMac can be upgraded to Catalina 10.15.7 but no later. See: How to download macOS - Apple Support
A mid 2014 and late 2014 iMac can be upgraded to the latest version of Big Sur macOS 11 but no later. See: How to download macOS - Apple Support
A late 2015 iMac can be upgraded to the latest version of Monterey macOS 12. See:How to download macOS - Apple Support
A 2017 or later iMac can be upgraded to the current version of Ventura macOS 13. See: How to upgrade to macOS Ventura - Apple Support
If you can't or don't want to upgrade the macOS, you may want to consider, for security reasons, using a 3rd party internet browser that supports running its current version on Catalina. One option is Chrome: https://www.google.com/chrome/