I've uploaded the board definitions for v1.3.x and v1.2.x of the nRF Connect SDK. Currently there is no support for the nRF9160 Feather in these versions of the SDK. Newer versions have them "built in".
For more info check out this link: https://docs.jaredwolff.com/nrf9160-compiling-app.html#board-defintion-files
This is now part of the normal SDK bringup process.