Abruptly lost the ability to use safari and access known sites, e.g. banking and xfinity email. I've tried to refresh safari but seems unsuccessful.

There was an issue with a recent update from Apple. Lots of posts in this fourm.

1) Check your version of Safari ( Menu Safari:About ) if it is 14.1 you may have the issue that impacted sites that use JavaScript..

2) Check the date of the Safari app in Finder Applications. If it is PRIOR to May 5th 2021 you need to update.

3) Go to System Preferences: Software Update and check for any updates. NOTE if you are NOT on Big Sur you do not need to upgrade to Big Sur. Look for updates for your OS. There is a link below the Big Sur update icon and link.

I have tested the latest version of 14.1 and it solved the issues I ( and many others ) wwere having with Safari 14.1.

I hope this helps

      Download EtreCheck, run it to see if there is any adware installed or not.

      https://etrecheck.com

      Click  “Free download” button,

      Open Downloads folder, click on it to open, and then select ”Open”.

      “Choose a problem” from the popup menu box, and then “Start EtreCheck” in the dialog.

      Click “Share Report” button in the toolbar, select “Copy report” .

      Paste the report when you reply.

      Note: This is a diagnostic test.