I've just updated to the lates firmware and it refers to instructions on fixed wing mode in manual version 1.6.

The manual in the app is v1.4.

Is it just me?

Mine has also v1.4 in iOS

Downlod it from dji.com.

Opened DJI GO4, selected Mavic, clicked academy then manuals and it is also V1.4.  I printed out the v 1.6 manual from DJI.com.  Samsung S7, Android 7.0, mavic and RC not connected

Righto.

Clearly it's too difficult for DJI to update the manual within the app at the time time as the firmware