Like other breakout teams, Girona might find it very hard to cope with the intensity of the Champions league. It's not the Spanish league where they were familiar with all the teams they went up against. All the elite teams play in the Champions league and Girona will have much more on their plates. It's not just girona, but teams that arw prolific in their domestic league don't usually do well in UCL. See the likes or Salzburg or Newcastle as you have mentioned. I'd like to think that teams like that mainly consider their UCL qualification as an achievement and anything after that — getting past group phase, knockout stages, eyc as a bonus. Not to mentioned thru have sold some of their best players.
Because next season Champion League will have new format i think to qualified to knockout stages is more difficult for the participant teams including Girona because at league phase they will fight against plenty of strong teams early from different countries so that's why i personally didn't expect more to Girona performance in this competition even most likely Girona will not able to qualified to round of 16
Besides Girona i would like to see the performance of other teams such as Leverkusen, Bilbao and Atalanta because last season their performance is really surprised us especially Leverkusen that they had just make records 51 matches unbeated which i am sure those records cannot be surpassed by other teams in the near future so i am curious want to see Leverkusen journey in this competition and do not forget too about Atalanta i think thy are dark horses team who has the potential to trouble the big teams