I cannot access banking websites with Safari on Macbook book ok with Chrome

Since you posted in the High Sierra forum it may mean that Safari is too far out of date to work with your banking websites. Apple hasn't updated Safari on High Sierra for at least six months now. You will need to use a third party web browser more and more often.

If your Mac is from 2012+, then you should be able to run a newer version of macOS. Here is a chart showing the compatible versions of macOS by Mac model:

https://eshop.macsales.com/guides/Mac_OS_X_Compatibility

If you find your Mac is able to run a newer version of macOS, then you can download the macOS installers from the links within this Apple article which also includes instructions for creating an optional macOS USB installer:

https://support.apple.com/en-us/HT201372

If your macOS can be upgraded, then make sure to have a good backup before attempting to upgrade macOS.

Go on the Apple certificate page:

https://www.apple.com/certificateauthority/

Download the Apple Intermediate Certificates

Apple IST CA 2 - G1 Certificate (direct download)

Double click the downloaded certificate to install it in Keychain Access.

You should see it now, in login certificates.

https://discussions.apple.com/thread/251211674?answerId=253087027022&page=1

As mentioned by earlier posting.

Have you tried using Safari with Developer Mode >> Safari Preferences >> Advanced tab and at very bottom Enable Developer in Menu Bar. One can change to Other Browser mode tricking the Bank Site into thinking the Safari is Firefox or another .