I tested NRF52840. but, I can't download it.
Are you using the pre-compiled hex file included in the SDK? Have you seen this issue with one of the other examples in the SDK, or is it only the blinky example you are having issues with?
Best regards, Joakim.
I using the pre-compiled hex file included in the SDK.
for the time being loading projects to the dongle using a softdevice is not supported by the nRF Connect for Desktop app. This will be added in the next release of the programming app. In the meantime you can achieve this through the use of nrfutil instead.