Transportation recommendations Zagreb to Venice to- Milan

I saw the same trip in the movie "From Russia With Love" but doubt you want to take that route (James Bond jumped off the train, made his way to the Adriatic by flower truck and stole a small power boat to cross the water to Venice). My Rome 2 Rio App shows that bus from Zagreb to Trieste with a train into Venice is 7 hours and about $47. A train route will take 10 to almost 13 hours to do the same trip.

Train from Zagreb to Ljubljana. Bus or shuttle from there to Venice (GoOpti, DRD, or FlixBus). DRD buses leave early in the morning, though. Spending a night in lovely Ljubljana isn't exactly a bad thing though you seem not to have much time for stops.

GoOpti claims they'll take you directly for 21 Euros per person (shared transfer), which seems like a great deal, actually, probably requires booking early to get that price. And they have a long window of the pick-up time (four hours when I checked just now) and you won't find out til the day before what the exact time is. But if you aren't tied to arriving in Venice at a certain time and can be flexible, this might be a very affordable option.

The ferry from Istrian towns in Croatia doesn't run every day by October, and it too leaves for Venice in the morning, I think.

Alternative is to take the train from Ljubljana to Trieste, and change there to another train to Venice. Trieste is well worth an overnight stay. The train from Ljubljana ends at the station of Villa Opicina. From there you take a tram to the centre of Trieste. Ljubljana to Villa Opicina is two hours; the same from Trieste to Venice.