If I understood it correctly your want to disable (grayed out) an option in a RadioGroup.

from vanilla import *

class Test:
    
    def __init__(self):
        
        self.w = Window((400, 400))
        
        self.w.allOptions = CheckBox((10, 10, -10, 22), "All Options", callback=self.allOptionsCallback)
        self.w.radioButtons = RadioGroup((10, 40, -10, 80), ["option 1", "option 2", "option 3"])
        
        self.w.radioButtons.getNSMatrix().cellAtRow_column_(2, 0).setEnabled_(False)
        
        self.w.open()
    
    def allOptionsCallback(self, sender):
        self.w.radioButtons.getNSMatrix().cellAtRow_column_(2, 0).setEnabled_(sender.get())
        
Test()

hope this helps