Microsoft will start automatically installing its new Outlook email app on Windows 10 devices. It's already pre-installed on most Windows 11 PCs and rolled out to some existing Windows 11 systems.

Windows 10 KB5050081 restores DAC support and pushes the new web-based Outlook app for all.(direct download .msu) ...

Designed to replace the current Mail and Calendar apps, the new Outlook can only be removed after it's been installed.

In other words, even if you can’t block the new Outlook app from being installed on your Windows 10 PC, you can always uninstall it afterwards. A pretty annoying move, but not as bad as it could be.