vscode Linux - mpi.h not found

Question

I cannot make VScode find the mpi header. I just created a minimalistic example:

#include <iostream>
#include <mpi.h>

int main(){

    std::cout<< "Hello World!!"<<std::endl;

    return 0;
}

My tasks.json:

{
    "tasks": [
        {
            "type": "cppbuild",
            "label": "C/C++: g++ build HELLO",
            "command": "/usr/bin/g++",
            "args": [
                "-fdiagnostics-color=always",
                "-g",
                "${file}",
                "-o",
                "${fileDirname}/${fileBasenameNoExtension}"
            ],
            "options": {
                "cwd": "${fileDirname}"
            },
            "problemMatcher": [
                "$gcc"
            ],
            "group": {
                "kind": "build",
                "isDefault": true
            },
            "detail": "Task generated by Debugger."
        }
    ],
    "version": "2.0.0"
}

launch.json:

{
    "configurations": [
        {
            "name": "C/C++: DEBUG HELLO",
            "type": "cppdbg",
            "request": "launch",
            "program": "${fileDirname}/${fileBasenameNoExtension}",
            "args": [],
            "stopAtEntry": true,
            "cwd": "${fileDirname}",
            "environment": [],
            "externalConsole": false,
            "MIMode": "gdb",
            "setupCommands": [
                {
                    "description": "Enable pretty-printing for gdb",
                    "text": "-enable-pretty-printing",
                    "ignoreFailures": true
                },
                {
                    "description": "Set Disassembly Flavor to Intel",
                    "text": "-gdb-set disassembly-flavor intel",
                    "ignoreFailures": true
                }
            ],
            "preLaunchTask": "C/C++: g++ build HELLO",
            "miDebuggerPath": "/usr/bin/gdb"
        }
    ],
    "version": "2.0.0"
}

c_cpp_properties.json:

{
    "configurations": [
      {
        "name": "Linux",
        "includePath": ["${workspaceFolder}/**", "/usr/lib/x86_64-linux-gnu/openmpi/include"],
        "defines": [],
        "compilerPath": "/usr/bin/gcc",
        "cStandard": "c11",
        "cppStandard": "c++17",
        "intelliSenseMode": "clang-x64"
      }
    ],
    "version": 4
  }

Note that I added the correct include path.

Hitting the debug Play button leads to fatal error: mpi.h: No such file or directory. If I remove the header inclusion, everything works fine. VSCode re-installation does not help.

C++ extension version 1.19.9 VSCode version 1.87.2 Ubuntu 20.04.6