Board files
The board definitions of the Icarus SoM Development Kit are included in the GitHub repository of Zephyr OS and can be found under boards/arm/actinius_icarus_som_dk/. 
To use the latest features in the nRF Connect SDK v2.1.x-v2.6.x and Zephyr OS, you can use the new Icarus board files which can be downloaded with the links below.
| nRF Connect SDK Version | Board Files Update Pack (BFUP) | 
|---|---|
| 2.1.x | BFUP-v1.4.0-nrf-2.1.x | 
| 2.2.x | BFUP-v1.4.0-nrf-2.2.x | 
| 2.3.x | BFUP-v1.4.0-nrf-2.3.x | 
| 2.4.x | BFUP-v1.4.0-nrf-2.4.x | 
| 2.5.x | BFUP-v1.4.0-nrf-2.5.x | 
| 2.6.x | BFUP-v1.4.0-nrf-2.6.x | 
Please extract the archive into the <ncs> directory of your SDK version. This is usually ~/ncs/<sdk-version>/.
You should be able to see folders like zephyr, nrf, bootloader in that folder.