The main hangup is probably around what year "24" should auto convert to being ambiguous as that adds an extra IF() to handle converting to 2024 instead of 1924. Beyond that it should just be =TEXTSPLIT(A1, "/") and =DATE(D1, C1, B1).
If I was going to drop my hackerman shades and pull up to an Excel code golf competition this is the "fewest total characters using a single cell" I could come up with: =REGEXREPLACE(A1 "^0?(\d{1,2})\/0?(\d{1,2})\/(..)?(\d{2})$", "20$3/$2/$1")
If I was going to drop my hackerman shades and pull up to an Excel code golf competition this is the "fewest total characters using a single cell" I could come up with: =REGEXREPLACE(A1 "^0?(\d{1,2})\/0?(\d{1,2})\/(..)?(\d{2})$", "20$3/$2/$1")