Can't include .H file in VScode "Undefined reference" C++

Question

Hardware: Raspberry pi 4

OS: Raspberry Pi OS

IDE: VScode

I am trying to include a FLTX library with (.H extension) to my .cpp file but I am getting a weird errors

Here is terminal output:

Starting build...
/usr/bin/g++ -g /home/pi/Desktop/CPP/test/test.cpp -o /home/pi/Desktop/CPP/test/test -l mosquitto -L /usr/include/FL/Fl_Window.H /usr/include/FL/Fl_Button.H
/usr/bin/ld: /tmp/ccHadCcX.o: in function `window()':
/home/pi/Desktop/CPP/test/test.cpp:72: undefined reference to `Fl_Window::Fl_Window(int, int, char const*)'
/usr/bin/ld: /home/pi/Desktop/CPP/test/test.cpp:73: undefined reference to `Fl_Group::begin()'
/usr/bin/ld: /home/pi/Desktop/CPP/test/test.cpp:74: undefined reference to `Fl_Group::end()'
/usr/bin/ld: /home/pi/Desktop/CPP/test/test.cpp:75: undefined reference to `Fl_Window::show()'
/usr/bin/ld: /home/pi/Desktop/CPP/test/test.cpp:72: undefined reference to `Fl_Window::~Fl_Window()'
/usr/bin/ld: /home/pi/Desktop/CPP/test/test.cpp:72: undefined reference to `Fl_Window::~Fl_Window()'
collect2: error: ld returned 1 exit status

Build finished with error(s).
The terminal process terminated with exit code: -1.

I have tried to make it work by following guides from the internet, but it didn't work

Here is some pieces of code from .cpp file:

//Here I include libs:
#include <FL/Fl_Window.H>
#include <FL/Fl_Button.H>


//And here they must be called:
void window()
{
    Fl_Window win(100,100, "test");
    win.begin();
    win.end();
    win.show();
}
//I call that function in main()

Here some more files that maybe will help: tasks.json:

{
    "version": "2.0.0",
    "tasks": [
        {
            "type": "cppbuild",
            "label": "C/C++: g++ build active file",
            "command": "/usr/bin/g++",
            "args": [
                "-g",
                "${file}",

                "-o",
                "${fileDirname}/${fileBasenameNoExtension}",
                
                "-l",
                "mosquitto",

                "-L",
                "/usr/include/FL/Fl_Window.H",
                "/usr/include/FL/Fl_Button.H"
                //"/usr/include/"
            ],
            "options": {
                "cwd": "${fileDirname}"
            },
            "problemMatcher": [
                "$gcc"
            ],
            "group": {
                "kind": "build",
                "isDefault": true
            },
            "detail": "compiler: /usr/bin/g++"
        }
    ]
}

and c_cpp_properties.json:

{
    "configurations": [
        {
            "name": "Linux",
            "includePath": [
                "${workspaceFolder}/**",
                "/usr/include",
                "/usr/include/FL",
                "/usr/local/include",
                "/usr/local/include/FL/images",
                "/usr/include/freetype2",
                "/usr/include/libpng16"

                //"/usr/local/include/FL",
                //"/home/pi/Downloads/fltk-1.3.6/"
                //"/home/pi/foo/fltk-1.3.2/"
            ],
            "defines": [],
            "compilerPath": "/usr/bin/gcc",
            "cStandard": "gnu17",
            "cppStandard": "gnu++14",
            "intelliSenseMode": "linux-gcc-arm",
            "compilerArgs": [
                "           "
            ]
        }
    ],
    "version": 4
}

And fltk-config stuff from terminal:

pi@raspberrypi:/usr/bin $ fltk-config --cxxflags
-I/usr/local/include -I/usr/local/include/FL/images -I/usr/include/uuid -I/usr/include/freetype2 -I/usr/include/libpng16 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -D_THREAD_SAFE -D_REENTRANT