What is the minimum number of symbols in preamble nRF52840 has to receive in order to receive full packet on Coded PHY? I can see that it can easily receive packet with less than 80 symbols received, but don't know what is the minimum here...
Sorry for the very late answer.
I'm not sure what you motivation is for asking this, but if you want to reduce the transmitted preamble, this would break with the BLE specification. It has to be 80us.
You will probably be able to receive a packet as long as the receiver sees 48 symbols of preamble. It is absolutely not recommend to use 48 symbols in the transmitter, this will have negative effects on sensitivity, radio performance and robustness.