I would personally avoid Mono, but I would use .NET Core. Core is not built for Windows alone.

https://stackoverflow.com/questions/37738106/net-core-vs-mon...

You are incredibly out of date. No one uses mono any more. It's .net core. The official version which works on multiple platforms.

Just last night I debugged some C# on Mac via Visual Studio for Mac. The debugger actually worked!

I must admit that I've been tinkering with this debugger for about 11 years. (Used to be MonoDevelop, then Xamarain Studio.) It used to be very unstable. Now it's usable.

YMMV

.NET Core has been running on multiple platforms for several years now, and many companies use it. I believe Bing itself is hosted on it as well. It's free and open source. They've been doing great work with performance.