There's a physical Fn keycap on the Raise, but Fn is not a function inside Bazecor.
On Windows and Linux, Fn works similarly to the Shift to Layer function in the Raise. For it to work, you need to assign the Fn key to a function, like Shift to Layer, using Bazecor.
On Mac, the Fn key is used to perform actions such as adjusting brightness and media controls. Sadly, we can't add such a key to the Raise, because Apple only allows Apple keyboards to have those keys. On the plus side, you can configure your Fn key to have any other function you want that's available in Bazecor.