here goes mine:
djokovic’s forehand (watch the 07 us open final and its not hard to notice how massive of a change it was)
wawrinka’s forehand (no need to comment here)
nadal’s forehand
federer’s backhand '17-'18 (that one is questionable, maybe its more due to the larger racquet frame)
slower courts and balls have made net game/ overheads practically irrelevant. i agree with you that his net game used to be atrocious and his overhead will probably never be sorted (same as mine lol, used to play junior ITFs, but mostly clay so i was somewhat fine), but given his playstyle i think the forehand change was more significant