PLC code generation produces a deployable vendor file from your project (PLCopen XML, Siemens Openness XML or SCL source, or Rockwell L5X). It runs through an export provider, so you need the matching vendor extension installed (CODESYS, Siemens, or Rockwell). Fanuc is translation only and is not a project-export target.
Using the button: click Generate PLC Output in the editor title menu.
Using the Command Palette: press Ctrl+Shift+P (or Cmd+Shift+P on Mac) and run AutomationView: Generate PLC Output.
To produce a single Sequence as vendor source text instead, use AutomationView: Translate to Target Language. See How to translate a Sequence.