This means the feature is unsupported, as in it is not receiving maintinance or development resources from the Core mbed OS team. This feature was at one point part of the supported featureset so some people may still be using it, as such we keep the code in the unsupported folder. Use things in the unsupported feature at your own risk as they either are not fully supported by all boards or are subject to removal from the mainline code in the future.
TLDR: Its the place for code we are no longer maintaining but someone may still be using.
If I try to include any header from “unsupported” folder it is not found during compilation. Shall I move code out of unsupported folder? Or is there any other proper way for including unsupported features into project?