CSHARP

dotnet target specific framework

// global.json file in root of your project (as far as I understand, 
// where you execute the 'dotnet' command, the CLI is going to go upwards
// until it finds this file and respect its contents - this means that it
// should not affect any other projects - even though its name is global.json)
{
  "sdk": {
    "version": "3.0.0"
  }
}