How to change visibility of external included source files?

Hi all,

I have an embedded project setted up that uses an SDK with external functionalities.
What I do is to add those as a library and then link respectively.
What happens in terms of the visibility on the IDE project tab is that they virtually appear near the project folder

It is not a problem itself but it makes the navigation a little bit annoying and confusing. These files are being processed with de CMakeLists.txt in the src folder, and it would make sense that these files should be visible there. Is there any way of doing that in CLion?

Besides (and this might be my lack of knowledge on CMake), the header files are visible to the project as I've included the directories with target_include_directories() but when I open the header file it says "This file does not belong to any project target, code insight features might not work properly."

So if the source file is visible and considered included in the project and the respective search path for the header files is also visible and navigable through the IDE, what this message means?

Thank you.