I am using the bootloader_secure_serial example from the SDK 14.0.0 on a 523832 DK. I have erased the device and flashed the softdevice and bootlader on it. The LED1 is turned on after restart, so the bootloader is in DFU mode.
I am having trouble testing the example with the nrfutil. I installed it using pip and tried running the command
nrfutil dfu serial -pkg name.zip - /dev/ttyUSB0 -b 115200 -fc 1
I get the "No ping response after opening COM port". Its not a problem with the UART or USB2UART module, as the ble_app_uart example is working fine on the same setup.