The 4 Global FX are send effects. These effects are used in the way that an input channel sends a signal to the effect. We also have channel FX that are in the same path as the eq, compressor etc. To get a chorus in the channel DSP chain you can change the DSP type.

If you change the preset DSP type for the guitar to a DSP type with chorus in the channel you can have the channel chorus  for the guitar and the doubler for the vocal.

You will have do redo your  eq, compressor etc. settings when you change the DSP type.

-Select the guitar stage icon

-Go to deep tweak mode

-Press the inspector icon to the left of the meter

-Press change DSP type

-Select a DSP type with chorus