Use relative path to point to precompiled .a library

This is showing the libraries in the PlatformIO sense. If you manually add a statically linked library via the build_flags, PlatformIO doesn’t recognize it. It would count it however if it were inside a proper library folder within lib/.

Wrong folder structure, you need to have `lib/pd_open_library/< the .a and the .json file>. See the reference tutorial I linked above which has

grafik

The paths in here must be relative to the library folder, not the root project folder. Doing a simpler

    "build": {
        "flags": [
            "-L.",
            "-llibPDlib.a"
        ]
    }

should suffice in this case. (The library is automatically added to the include path, so no -I is needed)