How to call public method in .NET5 dll from RapsberryPi using Python 3.9

Question

I have Win10 (64 bit) VS2019 C# .NET5 project. This project contains public method named "Add(int a, int b)" in public class "Calculate" in namespace "CsharpDll". Built end result is "CsharpDll.dll" file.

I am trying to call this "Add()" method from Raspberry Pi using RaspberryPi OS (32 bit) and Python 3.9. So far without success.

Note: "pythonnet" library does not support Python version 3.9. and installation will fail without attribute "--pre". Before running the Python code, I installed "pythonnet" library to Raspberry Pi using following command:

pip install --pre pythonnet

Here is the C# .NET5 sample I used:

using System;
namespace CsharpDll
{
    public class Calculate
    {
        public int Add(int a, int b)
        {
            return a+b;
        }
    }
}

Here is the Python sample I used:

#!/usr/bin/env python
import clr
from CsharpDll import Calculate

# set path variables
clr.AddReference('/home/.../CsharpDll.dll')

# create object
myDll = Calculate()
print('C# returned value: ', myDll.Add(1,2))

Expected result: C# returned value: 3

Actual result was an error message:

File "/home/.../.local/lib/python3.9/site-packages/clr_loader/util/find.py", line 67, in find_libmono
    raise RuntimeError("Could not find libmono")
RuntimeError: Could not find libmono

Question: Has anybody used .NET5 dll in Ruspberry Pi with Python 3.9, and have any ideas how to solve this issue?

Kindly Yours, Antti