Hi there,
There is an expansion board with additional FLASH on it for the smaller MCU’s devices. Grove expansion board, also the DFU can accommodate slots or pages for the OTA updates, ONLY in the NRF_SDK though. It works with the ALL of the Nrf5 series devices.
The nRF54 Series expands on that further allowing multiple slots and a ability to reStore old flash if the New code is a bomb.
Check out the Free webinar at Nordic for the specifics. 
HTH
GL 
PJ 