Flashing custom nRF52 (Bootloader, SoftDevice, Application)

Good morning,

Is it always required to use Segger J-Link in order to flash Bootloader, Softdevice and Application to a new device?

Could you summarize the different possibilities we have to flash any of these parts?

Furthermore, and regarding the nRF52840: is it possible to use the USB port to flash the device?

Best regards.