Path.Combine(string, string, string) doesn't seem to be available with .NET Framework 3.5

[eutro]

The changes to Starter.cs introduced here a41a224, specifically the use of the three-argument Path.Combine, doesn't work on a game I'm trying (Overcooked! 2) running .NET framework 3.5—the game just spams MissingMethodException: Method not found: 'System.IO.Path.Combine'. to the log. I'm not intimately familiar with .NET, but the documentation suggests that the method doesn't exist on 3.5: https://learn.microsoft.com/en-us/dotnet/api/system.io.path.combine?view=netframework-3.5.