As someone eager to start (properly) learning C#, is doing so on Mac actually viable? It sounds like it from your post but would be eager to hear your thoughts (I only have a Mac at home to practice on).
I've been doing C# on a Mac w/ Rider and it's been a delight. There's a few rough edges (using Windows/DOS style paths in the csproj breaks my muscle memory) but it's great.
Yes. VS Code is probably the easy button to get started. With a few plugins, it's ready to write, build, and debug C# projects.
I haven't built any production code in VS Code or .Net Core yet, but have started analysis for converting legacy .Net applications. I've also had interns doing some prototype work in .Net Core using VS Code, both on Macs and PCs. So far, so good.
I also used VS Code to do some React development. That worked out well also.
At this point, I'm hoping to get the legacy solutions converted in the next year or two, ditch my MSDN subscription, and move to VS Code full-time. Right now, I'm on a Mac, and running VS in VMWare.
Yes, Unity3d developers have been developing in C# on Mac for over a decade. Visual Studio for Mac (aka Xamarin Studio aka MonoDevelop) is better than Xcode in some respects.
I'm using a 2015 Macbook Air + vscode. Builds are fast, easy to debug code, even spinning up a local webserver to test my .NET MVC web app goes fast enough.