The good news is that the February update which brings the new Outlook doesn't strip out the old version of the app, so you can still use that.

Microsoft will force install the new Outlook email client on Windows 10 systems starting with next month's security update.

Just a few days ago, security researchers warned hundreds of millions of Windows users they’re at risk from a “ dangerous security fiasco .” Microsoft has now confirmed the same, proclaiming 2025 “the year of the Windows 11 PC refresh.” And for 400 million users in particular, that means hitting the stores before it’s too late.