So, you're not opening an email in Excel
That sentence puzzled me. Even if you're using Outlook/Office365, you open mails in Word, not in Excel.
"an email arrives with an Excel file that contains malicious macros"
That is the proper sequence of events. You get a mail from someone you've never met, download the attachment and leave your brain dead while you double-click it and ignore all warnings.
Because of course I'm going to open this attachment from some random stranger I've never met. He sent me this file, it must be important. What's the worst that could happen ?