I have a NodeMCU 1.0 (ESP-12E) board and the Arduino IoT Cloud website doesn't recognize the board. I have downloaded the latest Arduino Create Agent (version 1.2.3-b696989) and added the correct board type as my "Thing". I have inputted the network credentials and secret key in the setup.
However, on the "Sketch" tab it says "No associated Device Found" and I'm unable to upload the auto-generated code.
Opening the debug console via the Create Agent shows that my NodeMCU is recognized.
Another possibility is to download the code and upload it with the Arduino IDE. However, the current Arduino IoT Cloud library is not compatible with the newest ESP8266 platform. This has been discussed in the following post: Errors compiling ArduinoIoTCloud examples. The solution is to downgrade the esp8266 board platform to an older version. In the thread, pert suggests version 2.5.0 as it is used in Arduino Cloud. Doing some own testing it seems like all of the version below 3.0.0 work.