Flying in and out of Croatia, best airports

https://checkinprice.com/international-airports-in-croatia/

Above has list of airports with international service ( scroll down a bit)

Depending on where you end your Croatia travel, bus or rail may be an option

Zagreb may well have better international connections than Dubrovnik or Split. I flew from Zagreb to Washington DC with just one connection back in 2015. Zagreb is a very interesting city (to me)--quite different from the coastal towns. However, if you only plan to visit the coast, it won't be a very convenient landing point.

I use skyscanner.com to research intra-European flights. I don't know that you'll find many flights to Venice from either Split or Dubrovnik; I doubt that there's much tourist traffic from Italy to Croatia.

Folks ask how to connect Italy and Croatia fairly often here. I believe most end up using buses, trains, a shuttle or a ferry from Pula (in Istria) to Venice--or a combination of those.

You can begin exploring options on Rome2Rio.com, but just use it to figure out what might be possible, then dig down on that website to find the name of the transportation company operating the service you're interested in; go there for accurate information. Even during normal times, Rome2Rio is utterly unreliable in the fares, travel times and frequencies it displays.

Look for a multicity flight

arriving in Zagreb and departing from Venice

you can take a one way flight from dubrovnik to venice

that way you wont have to go back to zagreb for you final flight

When we were in Croatia there was ferry service to/from Venice from different cities.

In the fall of 2013, we flew KLM (no Croatia stop) into Venice Marco Polo (after several stops en route). Took a Croatia Airlines flight from VCE to Zagreb (ZAG) via Dubrovnik (DUB). There was no direct flight. Airline very good & price was right. Rented a car in Zagreb to cover Slovenia & Croatia. Dropped it in DUB. Left DUB for VCE on Croatia Airlines via Rome (FCO) with a transfer to Alitalia. Again no direct flight. A check of Croatia Airlines reveals you can't get a reasonable flight due to closed borders. Trains can normally get you from Venice thru Trieste & Slovenia to Zagreb, but when normal will occur is unknown. The train schedule was not optimal for us. Car rental from Italy to Croatia one way was too $$$ for us at that time. There may be a fast ferry from DUB to Venice (with stops) in summer 2021. Good luck.

In terms of size and ease of navigation, I'd add another vote for Zagreb. Small, easy to pick up bags and go, with good access to public transport and rental car options. We fly Lufthansa and for us, coming from Washington DC, connections are very good to much of Europe. Split is another smallish and perfectly acceptable airport, but there are fewer flights in and out, and the car rental desk area was a chaotic mess the day we were there. What's your planned itinerary? That could play the most important role in your transportation choices. For example, the ferry from Istria (Rovinj) to Venice is a pleasant trip in and of itself, and it gives a transportation option lots of travelers don't get, although it takes about 4 hours. It would be a nice way to move from Croatia to Venice, though. We found that from the US, the flights to Dubrovnik were not as plentiful as you would think since Dubrovnik is such a tourist magnet. That's what led us to change up the direction of our itinerary, starting in Zagreb, looping through Slovenia, back into Croatia and finishing up in Montenegro and Bosnia. Worked for us.

Zagreb and Split tend to have the most connections. As someone else mentioned, skyscanner is a good resource for flights. You can look at a "monthly" view for direct flights between cities. For example, you usually find direct flights only two or three times a week, so you need to plan around those dates. I don't recall ever seeing a flight to Venice, although we've flown from Split to Rome several times. There is a ferry line that travels up the Dalmatian coast to Ancona, Italy, but you would likely need to rent a car to get to Venice. If it were me, I would fly from Split to Rome, and then take a train to Venice. I often fly through Zagreb (connecting flight) to Zadar, which is a small but good airport.

With respect to seasons, there will be many more flights available in the summer. HTH.

*Just saw James' message. WOW! I did not know that EasyJet went to Venice. Good to know!

The Venezialines website tells you in English all about their fast ferries from northern Croatia (Istria) to Venice. I use them every year to get to Croatia from Marco Polo Venice airport (express bus to Piazzale Roma, #2 Vaporetto to San Basilio, Aperol Spritz in square near maritime terminal, leave for Rovinj at 5.15pm, there by dark). Some lines leave from Pula, I just prefer Rovinj or Porec. To get to Istria use bus or planes. Croatia Airlines usually flies from Zadar (wonderful place) to Pula, for example. Ditto from Zagreb, so maybe you can plot a flight from Dubrovnik to Zagreb (well worth several days) and on to Pula. The express bus Zagreb to Pula (see Arriva website) is only 3.5 hours and very scenic. As are all of the new buses.
Caveat - as things change constantly, you may want to follow developments on a Croatia site like Total Croatia News. The new entry form may still be required and can be viewed on Enter Croatia. Right now, you need to prove hotel reservations, for example.

Most airports publish a timetable for upcoming flights, both in and out. Split Airport usually does this but it's out of date, probably due to the virus. We flew in and out of Split in June a few years ago and found the process easy. They've recently expanded the airport terminal to cope with late summer traffic - many services are indeed seasonal. The same with Dubrovnik, but Zagreb has more year-round connections. Split has ferry service to Ancona, and you can get to Venice form Ancona by train.

You might check Tivat and Podgorica too. Croatia doesn't have great connectiins..

When I plan a trip I use Google Flights. So reaching Venice is the goal so you choose From Venice to Europe, one way, non stop. A map comes up showing all the flights that meet the criteria. But you need to be flexible and look at different days ofconnections.

Then there is the what is going on now means a lot of flights and connections are canceled or on hold. This is probably best done a few months before you leave.

Zagreb is probably your best shot as it's also closest to venice, but you didn't state what you want to do in Croatia? they say a trip to Croatia without visiting Split or Dubrovnik is a missed opportunity but that is not so true.. you can spend family trips on the island of Cres, Krk, Opatija and the Istrian side and have a great time too.