Hello again,
I have merged two projects as described here:
https://devzone.nordicsemi.com/f/nordic-q-a/67575/serial-communication-usb-with-ble-hid
My application works on the DK, however, when flashing it (with the adjustments I'll describe next), it does not advertise any HID on Bluetooth and does not open a serial COM port in the device manager.
Adjustments I made:
Adding those two lines to main.c:
#define TX_PIN_NUMBER 6 #define RX_PIN_NUMBER 8
as described here https://devzone.nordicsemi.com/nordic/short-range-guides/b/getting-started/posts/nrf52840-dongle-programming-tutorial , I adjusted the memory layout of the resulting hex.

I then flashed only the resulting hex on the Dongle, which results in the following memory layout:

0x0 - 0xFFF MBR
0x1000 - 0x2466F Application
0xE0000 - 0xFDFFF Bootloader
I think that my project already includes a softdevice, as when I'm trying to add the s140 hex I get the following error in nRF Programmer:

Any ideas?