GetFormattedTypeName.cs

using System;
using System.Collections.Generic;
using System.Linq;

Console.WriteLine(GetFormattedName(typeof(int)));
Console.WriteLine(GetFormattedName(typeof(decimal?)));
Console.WriteLine(GetFormattedName(typeof(IEnumerable<List<string>>)));
Console.WriteLine(GetFormattedName(typeof(Dictionary<int, string>)));

static string GetFormattedName(Type type)
{
    if (!type.IsGenericType)
        return type.Name;
    
    var names = type.GetGenericArguments().Select(GetFormattedName);
    var genericArguments = string.Join(", ", names);
    var underlyingType = type.Name.Substring(0, type.Name.IndexOf("`"));
    
    return $"{underlyingType}<{genericArguments}>";   
}