Arriving end of June, late night. unsure when the airplane will land, get through customs, passport, etc. Going to Luxembourg Garden area. Is Noctilien bus a good choice? or Uber? or taxi?
Noctilien buses are quite infrequent, but do run throughout the night if you are willing to wait.
You can check for 140, 143 night bus schedules from CDG to Gare de l'Est here:
You'd still need to make your way to Luxembourg area after arriving at Gare de l'Est which is on the Right Bank (other side of the Seine River from Luxembourg area).
After a long flight, arriving at night, with significant brain fatigue, taxi is perhaps the better option, with flat rates to the Left Bank (southern half of Paris centre) at 58 euros.