Seeed Studio XIAO nRF52840 Sense - Writing data on the onBoard flash memory

Hi everybody,

I would like to write a .wav file that I would have recorded with the microphone of the Seeed Studio XIAO nRF52840 Sense.

I found the following code that would allow me to write on the internal memory:
Read Write Flash

I see the following specs:
256 KB RAM,1MB Flash 2MB onboard Flash

That’s the memory of the nRF52840:
Flash: 1 MB
RAM: 256KB

Is it possible to write on both the 1MB Flash memory and the 2MB onBoard flash memory ?
Or is the 1Mb Flash memory reserved for the microcontroller ?
If it’s possible to use both, how do you differentiate which memory you are writing to ?

I’d welcome any insight.

Thank you.