Apple Mail Smart Mailboxes not working after update to Sonoma 14.3.1

After updating my 15" M2 MacBook Air to Sonoma 14.3.1, my Apple Mail Smart Mailboxes no longer function. They do not show the mail items they are set to show, such as Unread Mail or Today's Mail, etc. What they do show is whatever list of mail was showing in the Viewer Window before selecting the Smart Mailbox.

For instance, suppose I have a normal mailbox named "Joe" where I store mail from my friend Joe, and I select it and look at the list of mail from Joe that I have retained there. When I select the Smart Mailbox "Unread Mail", instead of showing any unread mail from my various inboxes, it will show the list from the mailbox "Joe". And all the other Smart Mailboxes will show the list from "Joe" as well. And if I then look at the list of mail in the normal mailbox "Sam", any Smart Mailbox I select will then show the list from "Sam".

I have quit Mail, restarted my Mac, made new Smart Mailboxes and the problem persists. Has anyone else experienced this issue? Any suggestions are greatly appreciated.