Can I use Nordic Soft device with BL5340?

Answer

nRF5 SDK SoftDevices are incompatible with the nRF5340 and there is no plan for any compatible release. The nRF5340 is designed to be used with the nRF Connect SDK (NCS), with either the Nordic SoftDevice Controller (not to be confused with the nRF5 SDK SoftDevices) or the Zephyr Bluetooth LE Controller (open source) as Bluetooth link layer. 
 
From <https://devzone.nordicsemi.com/f/nordic-q-a/76662/nrf5340-soft-device-backward-compatibility>