Data Matrix Code decode returns result null value

[RadovanPodhradsky]

I tried to use several appraches to decode DMC generated by online generator https://barcode.tec-it.com/en/DataMatrix which I used with real scanners (Datalogic or Cognex) before. Generated DMC I saved to .bmp or .png files and tied to load using

Bitmap barcodeBitmap = (System.Drawing.Bitmap)System.Drawing.Image.FromFile(dmcFilePath);

or

Bitmap barcodeBitmap = new Bitmap(dmcFilePath);

images are shown properly with

pictureboxBarcode.Image = barcodeBitmap;

I tired these 2 option to decode DMC in bitmap, both returns null result from Decode/decode methods:

    public static string DecodeDataMatrixCode(Bitmap bitmap)
    {
        IBarcodeReader reader = new BarcodeReader()
        {
            Options = new ZXing.Common.DecodingOptions
            {
                PossibleFormats = new List<BarcodeFormat> { BarcodeFormat.DATA_MATRIX }
            }
        };

        var result = reader.Decode(bitmap);
        return result?.Text;
    }

    public static string DatamatrixDecodeDataMatrixCode(Bitmap bitmap)
    {
        DataMatrixReader reader = new DataMatrixReader();
        BitmapLuminanceSource luminanceSource = new BitmapLuminanceSource(bitmap);
        HybridBinarizer binarizer = new HybridBinarizer(luminanceSource);
        GlobalHistogramBinarizer binarizer1 = new GlobalHistogramBinarizer(luminanceSource);
        BinaryBitmap binaryBitmap = new BinaryBitmap(binarizer1); // I tried binarizer too, result of decode was null

        // Set up the hints
        var hints = new Dictionary<DecodeHintType, object>
        {
            { DecodeHintType.TRY_HARDER, true }
        };

        Result result = null;
        try
        {
            result = reader.decode(binaryBitmap, hints);
        }
        catch (Exception f)
        {

        }

        return result?.Text ?? "(null)";
    }

testing form usings:

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Drawing;
using System.Windows.Forms;
using ZXing;
using ZXing.Datamatrix;
using ZXing.Common;

.NET Framework 4.8 WinForms testing application with ZXing.Net 0.16.10 nuget installed by NuGet Package Manager.

Dooes somebody have some hints/recommenndations how to decode DMC code generated by

https://barcode.tec-it.com/en/DataMatrix?data=a1234567890112233020250206

successfully?