Get PHPMailer working with SMTP on Microsoft 365 Exchange Server

I have a PHPMailer script that has been working over a decade. It successfully sends emails with SMTP. The problem: some of my clients have migrated their email accounts from our hosting companies to Microsoft 365 Exchange servers. And all PHPMailer emails fail for me with Microsoft 365 Exchange. I need a solution. I'm hoping it's simply a matter of tweaking some of the parameters.