update browser

how to check for updates

Keep your Mac up to date - Apple Support

if it says it is update then you may wish to upgrade to 10.14 or 10.15

How to upgrade to macOS Catalina - Apple Support

if you mac is too old to support newer versions of macos then you should maybe try another browser

As to your question, i am going to assume that your browser is Safari. Safari, being installed as part of the operating system, normally it cannot be individually upgraded. it is periodically updated when the computer's operating system is updated or upgraded. This is not an unusual complaint from your bank. Web site engineers write their software to work with specific browsers. For some reason, they often choose to not be compliant with Safari. This is not an Apple problem as Apple has no control over the millions of web sites on the internet. As noted above, you can check for updates. If an update is available and installed, that will not automatically mean that the browser will be compliant with the bank's web site. You can hope that your web site's developers eventually update their site to work with Safari, or you can use another browser that does work, such as Firefox or Chrome. Good luck to you.

Try this browser...

https://brave.com/