Transportation from Venice to Rovinj

Here's the ferry schedule and I hope you are there early enough in Oct to do it .
https://adriatic-lines.com/venice-to-croatia-ferry/

I went in the other direction -Rovinj to Venice. Did the bus from Rovinj to Trieste. There was the border crossing in Slovenia and we had to get out of the bus, walk through the customs checkpoint and then get back on the bus. This to me unexpected process made me miss my train to Venice and my meetup with an Italian cousin. Then continued on to Venice on a later train. Rovinj is fabulous.

As of 1/1/23 Croatia has joined the Schengen zone so there is now an open border between Croatia and Slovenia. However, it is possible there still may be border checks from time to time for security reasons.

You might want to see if GoOpti shuttle is an option. In 2018 5 of us traveling together booked GoOpti for the trip from Ljubljana to Venice. It was reasonably priced and a fast and pleasant way to travel. Of course to Rovinj travel by water could be faster and cheaper.

Ferry is definitely the best way to go. I have done this myself, and there is something special about arriving in a country on a boat.
The ferries are scheduled to be of use to people vacationing in Istria that want to do a day trip to Venice. So the go to Venice in the morning, and return in the evening. In my case I had just taken a train to Venice, and there walked to the Stazzione Marritime San Basileo, bought my ticket there, and then spend a few hours in Venice.

There are several companies that do this. Expect schedules to be made available later. In my case I was travelling in September there were three returns to Rovinj that evening, and I just picked the fastest...

Ferry is definitely our 1st choice—just not sure they will be running in early October. Looking at all options! Appreciate the input.