Does a man's admiring gaze at a woman in tight or short clothing, without lust, invalidate ablution, and does touching a woman invalidate ablution even if it is with pleasure?

Looking at a woman, whether with or without lust, does not invalidate ablution, unless it leads to emission, in which case ablution is invalidated by the discharge, not by the gaze. It is forbidden to intentionally look at a non-mahram woman, but an accidental glance is excused, and one must avert their gaze from her. As for greeting a non-mahram woman without shaking hands, its ruling regarding the invalidation of ablution is the same as that of looking. If the intention of greeting is shaking hands, then the answer to that has already been provided in Fatwa no. 2248.