RAK4631 and RAK19007 with RAK5860, Arduino BSP.
The RESETREAS register gives 0 regardless of the restart reason (cold start, coming back from deep sleep, reset key).
I’m reading & saving the contents right at the beginning of the init sequence:
// Read once
g_resetreas_snapshot = NRF_POWER->RESETREAS;
// Clear hardware bits after reading
NRF_POWER->RESETREAS = g_resetreas_snapshot;