There is nothing wrong with your Mac's version of Safari, but Chase Bank's website will refuse to function with it. It the only institution with this problem. They need to stop using the outdated and privacy-intrusive "user agent" query as the means to determine if a browser can handle their website, which was never a good idea to begin with.
Unfortunately, that leaves you out in the cold until they realize the error of their ways and correct it.
The workaround for end users who are unable to update their Macs to a newer macOS version is to use a different browser.
Consider Brave:
https://brave.com/
Firefox is a distant second choice:
https://www.mozilla.org/en-US/firefox/new/
The bottom line is that there is nothing wrong with your Mac's version of Safari, but that bank is using an outdated and ill-conceived method of determining browser requirements. If you are so motivated direct their attention to the WWW publication User-Agent Client Hints (courtesy VikingOSX).
In-depth background discussion here: chase wants me to update safari to 16, should I do that? - Apple Community