How to Inject DLL into ANY process?

I'm working on way to inject a dll into any process on windows. I already have a code that work for my own program, like hello world or thing like that but other programs, like notepad , calc, chrome, etc..

Program can prevent the injection of dll, so I don't know what I can do to bypass this.

My final goal is to hook the api call of any program.

This domains is new for me, so I'm a beginner here, if you have any resource or solution about it !

injector.cpp

#include <iostream>
#include <Windows.h>

int main()
{
    // path to our dll
    LPCSTR DllPath = "D:\\projects\\standardinjection\\release\\testlib.dll";

    INT process_id = 14367;
    // Open a handle to target process
    HANDLE hProcess = OpenProcess(PROCESS_ALL_ACCESS, FALSE, process_id);

    // Allocate memory for the dllpath in the target process
    // length of the path string + null terminator
    LPVOID pDllPath = VirtualAllocEx(hProcess, 0, strlen(DllPath) + 1,
        MEM_COMMIT, PAGE_READWRITE);

    // Write the path to the address of the memory we just allocated
    // in the target process
    WriteProcessMemory(hProcess, pDllPath, (LPVOID)DllPath,
        strlen(DllPath) + 1, 0);

    // Create a Remote Thread in the target process which
    // calls LoadLibraryA as our dllpath as an argument -> program loads our dll
    HANDLE hLoadThread = CreateRemoteThread(hProcess, 0, 0,
        (LPTHREAD_START_ROUTINE)GetProcAddress(GetModuleHandleA("Kernel32.dll"),
            "LoadLibraryA"), pDllPath, 0, 0);

    // Wait for the execution of our loader thread to finish
    WaitForSingleObject(hLoadThread, INFINITE);

    std::cout << "Dll path allocated at: " << std::hex << pDllPath << std::endl;
    std::cin.get();

    // Free the memory allocated for our dll path
    VirtualFreeEx(hProcess, pDllPath, strlen(DllPath) + 1, MEM_RELEASE);

    return 0;
}

my dll

#include <Windows.h>

BOOL APIENTRY DllMain( HMODULE hModule,
                       DWORD  ul_reason_for_call,
                       LPVOID lpReserved
                     )
{
    if (ul_reason_for_call == DLL_PROCESS_ATTACH)
        MessageBox(0, L"Hello From testlib!", L"Hello", MB_ICONINFORMATION);

    return TRUE;
}

I'm currently on windows 10 x64 Coming from Unix os, so Windows is pretty new for me!

Thanks for your time !