The following excerpt from this Discussion may be of interest to you:
"I think that financial institutions that base their security criteria on the current UA header string will be prematurely blocking browsers until they adopt these new W3C approach to identifying the correct browser and associated data content."
(Courtesy VikingOSX)
Your bank is likely to be one of them. It's them that need to change — not you.
The back story is most likely due to Apple's considerable sensitivity to protecting user privacy. Apparently, the "User Agent" query (which was always ill-advised) has been alleged to contribute to passive fingerprinting — one of many devious ways of tracking your Internet activity. So the "user agent" in this case is reporting a browser that is indeed out of date, but which may very well be compliant with all relevant security protocols.
In any event that is a long-winded way of saying "try another browser". I recommend Brave, or Firefox, and in that order.
https://brave.com/
https://www.mozilla.org/en-US/firefox/browsers/