Hello Carolyn!
If I understand correctly, you’re having trouble accessing a specific website using Safari due to trusted certificates. Is that correct? I’ll be happy to advise.
How long has this been an issue?
Has there been any recent changes made on your Mac before experiencing the issue?
Does this seem to occur with multiple websites, or just the website you mentioned specifically?
Have you tried clearing your history and restarting your Mac to test?
Take a look: Clear your browsing history in Safari on Mac
You can also try changing the trust settings to the certificate as well.
Change the trust settings of a certificate in Keychain Access on Mac
Try the steps in these articles as well:
If Safari doesn't load a page or webpage items are missing
If Safari is slow, stops responding, quits unexpectedly, or has other issues
Keep me updated on the results.
Cheers!