Split to Venice

Are you thinking as a day trip? Or the next stop on a longer trip?
And yes it is a PIA to get there from Split. Once you start going north in Croatia, your travel options lessen.

Venice is to far from Split for a day trip. Its a seven hour drive by car...

You can take a cruise from Venice along the Croatian coast to many places including Split and return from Dubrovnic, or in the reverse direction.

According to Direct Ferries website: https://www.directferries.com/global/index.html there are no ferries from Split to Venice. There are ferries from Rovinj to Venice that is north of Split taking 3h.

Of course it’s too far for a day trip! But some people might not realize it. I should have put that in my response.

No, not a one day trip. I was hoping to go to Venice for couple days after a week in Croatia and fly back to US. I thought maybe there is a direct ferry or train that does not take too long.

Depending on the time of year you can take the old classic Marco Polo ferry from Split to Ancona and take a modern fast train up to Venice. Check ferry and train websites.
The train won't stop so the crew can have lunch on the opposite platform. as it did when I took it 50 years ago, but hey.
The Marco Polo ferry used to run up and own the coast, Last of the old ferries.
Obviously this is not a day trip but it might be nice way to go to Venice. Take the train right into Santa Lucia station unless you have booked a hotel in Mestre half an hour north. Which many people do. And any Veneians live in Mestre, not Venice.
Yes, there is still one ferry line Atlas Compass from Rovinj to Venice, but that is another story.
Check all travel schedules as the season winds down, of course.

Thank you for your recommendations. I have decided that it would be too far and too long to get to Venice . Will have to be a separate trip.