Is wearing elegant and clean clothes considered arrogance, especially if it increases self-confidence and leads to a tendency to flirt with girls and approach them emotionally and intimately? And is this Haram?

There is no harm in wearing beautiful and clean clothes, and that is not part of the arrogance which is rejecting the truth and despising people. However, one should avoid extravagance and indulgence. What you mentioned about your self-confidence, your emotional sensitivity, and your inclination to flirt with girls may be due to conceit, in addition to the impermissibility of flirting with girls. The problem is not in clothes and elegance, but in the self. Therefore, you must cure yourself of conceit and flirting with non-mahram women to be among the successful, for "He has succeeded who purifies it [the soul]."