Maybe there are additional solutions but with this settings it works for me.
MSFS2020, Visual Studio 2019 vb .net, c# and c++. .net framework > 4.7.2 or 4.8
Target x64
Copy "Microsoft.FlightSimulator.SimConnect.dll", "SimConnect.dll" and "SimConnect.lib" to the directory ...\<your project>\bin\x64\Debug and ...\<your project>\bin\x64\Release
Add reference to "Microsoft.FlightSimulator.SimConnect.dll" to your project.
MSFS2020, Visual Studio 2019 vb .net, c# and c++. .net framework > 4.7.2 or 4.8
Target x64
Copy "Microsoft.FlightSimulator.SimConnect.dll", "SimConnect.dll" and "SimConnect.lib" to the directory ...\<your project>\bin\x64\Debug and ...\<your project>\bin\x64\Release
Add reference to "Microsoft.FlightSimulator.SimConnect.dll" to your project.