Example of net48 target from sdk style project.

Example.txt

PS C:\dev\source\repos\SdkStyleNet48\SdkStyleNet48> dotnet run
Hello, World from 4.0.30319.42000!
PS C:\dev\source\repos\SdkStyleNet48\SdkStyleNet48> dotnet build
MSBuild version 17.7.3+8ec440e68 for .NET
  Determining projects to restore...
  All projects are up-to-date for restore.
  SdkStyleNet48 -> C:\dev\source\repos\SdkStyleNet48\SdkStyleNet48\bin\Debug\net48\SdkStyleNet48.exe

Build succeeded.
    0 Warning(s)
    0 Error(s)                                      
PS C:\dev\source\repos\SdkStyleNet48\SdkStyleNet48> ildasm .\bin\Debug\net48\
// Metadata version: v4.0.30319
.assembly extern mscorlib
{
  .publickeytoken = (B7 7A 5C 56 19 34 E0 89 )                         // .z\V.4..
  .ver 4:0:0:0
}

Program.cs

using System;

internal class Program
{
    private static void Main(string[] args)
    {
        Console.WriteLine($"Hello, World from {Environment.Version}!");
    }
}

SdkStyleNet48.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net48</TargetFramework>
  </PropertyGroup>

</Project>