How to update Safari on my Mac?

Upgrading macOS installed on your Mac is an option.

How to get old versions of macOS

If your Mac isn't compatible with the latest macOS, you might still be able to upgrade to an earlier macOS, such as macOS Catalina, Mojave, High Sierra, Sierra, or El Capitan.

https://support.apple.com/en-us/HT211683

To be clear, Safari is normally not able to be updated individually. It is installed as part of the Mac operating system. That must be updated to update Safari.