Hard to give a hint on the theme this time without giving it away altogether. Different kind of them. Not related to the long answers at all (well, there aren’t any long answers, really) 38-Down and 69-Across and 56-Down are “key” clues that relate to the theme, but I’d guess you’ll discover the trick of the puzzle before you get those. You’ll get the idea when you find what should be an answer but seems to be missing something important. No, not a rebus (multiple letters in the same box). Haven’t seen this idea before. Once you get one, the rest will fall into place. Usually you shouldn’t get too edgy, but it might help you with this one.
10 specific hints:
39-Across Less certain: somewhat slangy
59-Across French children’s song: that most American school kids learn. Rhymes with 84-Across
78-Across Old fashioned street conveyance: two words. kind of self-contradictory
122-Across Jumping off point: quite appropriate for this puzzle!
111-Across Honor at graduation?: Not sure why there’s a question mark on this one. Oh, cum now!
108-Down Big screen format: Really big!
41-Down Pope Francis’ birthplace: No, not Assisi, he was a saint, not a pope. Pope Francis is the current pope, in case you didn’t know.
70-Down Fleur-de- : I can never remember if this is the one with the “Y” in the middle (it isn’t!)
54-Down ______ Light: think commercial product
112-Down Org. in “Monk”: 4-letter acronym