FTN95 can produce code that is compatible with all versions of .NET that runs on Microsoft Windows (note that .NET 1.1 code is also .NET 2.0 compatible and .NET 2.0 code is.NET 4.0 compatible) via Visual Studio. The target framework can be selected from the project properties.
If you use the command line then you will have to set a switch to target a particular framework:
|.NET 2.0||/CLR /CLR_VER 2||dbk_link2|
|.NET 3.0||/CLR /CLR_VER 2||dbk_link2|
|.NET 3.5||/CLR /CLR_VER 2||dbk_link2|
|.NET 4.0||/CLR /CLR_VER 4||dbk_link4|
|.NET 4.5||/CLR /CLR_VER 4||dbk_link4|
The reason you have to specify the .NET framework is that many people have multiple versions on their machine, probably without realising. In addition, you need to use a different linker for .NET 2.0 (dbk_link2) and .NET 4.0 (dbk_link4) because the linker runs under the destination framework to produce the final code.
.NET 3.0 and .NET 3.5 is .NET 2.0 with extra libraries -- hence you just use the .NET 2.0 support for those version.
To debug .NET 4.0 code you will require Visual Studio 2010, 2012, 2013, 2015, 2017 or 2019.
To use any framework, that version's directory must be on the path.