Safari version 13.1.2 on macOS high Sierra, browser not working to sign into Citi.com. how do I get newer safari browser?

Hello jemagaro,

Since Safari is an integrated part of macOS, you would need to upgrade macOS in order to update Safari. Depending on your model, you can use the applicable resource below to see if your Mac is compatible with a newer version of macOS:

Identify your MacBook model - Apple Support

Identify your MacBook Air model - Apple Support

Identify your MacBook Pro model - Apple Support

Identify your iMac model - Apple Support

Identify your Mac mini model - Apple Support

Identify your Mac Pro model - Apple Support

If your Mac is compatible with a newer version of macOS, the details from this resource can help with the upgrade process: How to download and install macOS - Apple Support

Should you have any further concerns, don't hesitate to let us know.

Please read Update to the latest version of Safari - Apple Support. If you are unable to upgrade macOS then your options are to use a browser that placates the websites complaining it's too old.

Consider Brave:

https://brave.com/

Firefox is a distant second choice:

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

Both will run on High Sierra, but just be advised both of them are approaching their end of life also. If your Mac is too old to run a later macOS version, eventually you will need a newer one.