Is there any software update for older iMac 12 years old?

Safari is updated when you upgrade macOS.

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. See: How to download macOS - Apple Support

For security reasons it would be a good idea instead of using an outdated Safari to use a 3rd party browser that supports running their current version on your macOS version.

The current version of Chrome will run on macOS 10.13 or later: https://www.google.com/chrome/

The current version of Firefox will run on 10.12 or later: https://www.mozilla.org/en-US/firefox/

Mostly you just need a more modern Browser than Safari on High Sierra like Firefox or Brave.

https://brave.com/

https://www.mozilla.org/en-US/firefox/83.0/system-requirements/

Firefox 83.0 System Requirements (mozilla.org)

Thanks to dialabrain…

FWIW, Firefox 109.0 (current version) runs in High Sierra.

https://www.mozilla.org/en-US/firefox/new/

Not from Apple. If you use a third party browser you may some still provide updates.