You generally cannot "downgrade" Harmattan firmware. Always ensure you are flashing a version equal to or higher than your current version.

The N9 is a piece of history—upgrading its software is the best way to ensure it doesn't just sit in a drawer, but stays in your pocket.

Before installing a custom ROM, users must ensure their Nokia N9 meets the necessary requirements:

The Nokia N9, released in 2011 with the Linux-based MeeGo Harmattan operating system , remains a cult classic in the mobile world. Because official support ended years ago, installing a custom ROM is the primary way to "resurrect" the device for modern use. Notable Custom ROMs for the Nokia N9

There is always a risk of bricking older hardware.