Where should someone start if they wanted to get familiar and proficient with .NET?

Check out F#, the bastardized yet legitimate child of MSFT.

If you like functional languages or would like to try it, give it a whirl!

https://dotnet.microsoft.com/learn/languages/fsharp-hello-wo...

If you use vscode, highly suggest to use Ionide extension. You’ll be quickly amazed at how smooth it all works.

F# is cool, but definitely not where to start. C# is by far, by far, by far the most popular .net language

Depends on what OP is familiar with. If they know/like functional programming, I'd recommend F# highly. If not... Yeah go with C#.

Then later learn F# because it's absolutely kick ass :)

An experienced functional programmer can learn F# in a minute, which is fine for console programs. But I tried to write a basic GUI program in F# on Linux and gave up after I reached my googling limit.