Their first season in this competition is more about gaining experience and understanding the intensity of competition that takes place in the UCL with against big teams, so indeed they can't do too much in the UCL when facing strong teams, like as Feyenoord, PSG and eindhoven who have experience and better performance in the UCL, however, like your said, the experience Girona have gained from UCL games this season will be invaluable for their future development, although there is no guarantee that they will be able to qualify for the UCL again if remember their inconsistent form in La Liga so far.
Girona is 30th in the standings with 3 games left to play and clearly has a chance of less than 5% to enter the play off round. For that reason Girona can only play as hard as possible without taking risks, because the clubs above them will also compete to win the play-off zone. But if Dovbyk is still there, maybe Girona performance will be a little better in the UCL.