I don't believe it. That's the same Mono/Winform page from 2015, and at the time their "complete support" only meant "will probably compile." From my experience Mono is primarily intended to make programs developed on Linux easy to port to Windows, but trying the reverse is a quick way to discover that some functions behave differently or worse are just placeholders that throw runtime exceptions on execution.
Maybe things are better in Mono 5.x, but even if Aurora C# had compatible winform coding the map rendering code would probably still need to be ported.
In summery anyone who thinks Mono is an easy transition to other OSs should join the Pulsar 4X project. The original group broke apart partially over system incompatibilities, and those continuing have been asking for fresh blood. Granted, half our problems were OpenGL compatibility issues rather than cross-platform WinForm/Mono issues, but still.