I don't have skin in the game, but at least the .Net way is quite explicit, which I like:
byte[] unicodeBytes = Encoding.UTF8.GetBytes(inputString);
// Perform the conversion from one encoding to the other.
byte[] asciiBytes = Encoding.Convert(Encoding.UTF8, Encoding.ASCII, unicodeBytes);
string outputString = Encoding.ASCII.GetString(asciiBytes);
Adapted from https://learn.microsoft.com/en-us/dotnet/api/system.text.enc...