Arriving in Venice from US and then flying to Naples - do I have enough time???

It's risky. Can you do carry-on? If you'll have your bag and boarding pass for 2nd flight in hand, then it's a definite maybe.
If the first flight is late, or you encounter a long line (both happen), then it gets real iffy.
It's not the passport check that I would worry about, it's waiting for a bag. If they somehow lose the bag (it happens), then another woe.
Naples airport transport links: https://www.aeroportodinapoli.it/en/

If it was me I'd change the flight and go to Rome or (even better) Naples. It would be worth the change fee IMO.

How many ways can your plan go wrong? Here's a few. RyanAir closes boarding 30 minutes before the flight, so now you have 1.5 hours (assuming the flight is on time) to deplane,, clear immigration, get your luggage, clear customs, go back thru security and get to the gate. But there's more. I assume you need to check your bag because you're checking it on the flight from the US. RyanAir closes bag check 40 minutes before their flight. Or you can take the bag to the gate for an extra fee. And keep in mind nobody is stricter about each and every rule than RyanAir. They will check your bag dimensions and weight. If they don't meet the rules then it's a trip to the Oversize Baggage Desk, which of course will take more time.

When you're at the Naples airport take the bus to Sorrento, it goes to the front of where the train would have taken you.

That is a tortuous day even if you weren't jet lagged. The Naples to Sorrento commuting involves a gritty commuter train which may only have SRO and no air conditioning. Buses kind of run on a suggested schedule. Moving about in Naples and areas south involve using severely neglected transportation "systems" which cannot handle the demand. Buses run on very congested roads. This is not like using the transportation systems in northern Italy. Things just don't work well. The ferries are weather- dependent and are often canceled during bad weather. You also need to be alert regarding pick pockets.

Spend the night in Venice, then train to Naples the next day when you're rested. Then you are better able to accept the realities of getting to Sorrento. Perhaps hire a private driver from Naples to Sorrento, but that still could take two hours.

You are visiting a beautiful area that is a victim if it's Instagram success, and is very crowded. Being prepared for the realities on the ground will contribute to a more enjoyable trip.

Good luck!.

Flying on major airlines was far more uncivilized in my experience versus buses in this area--it is the tight connection that is problematic. Tons of people take the direct from airport bus, so don't worry about that. If you actually make the flight, you will be so relieved and exhausted that you won't care!
But I'd try to change the flight, it's that or hang out in the airport longer and who wants that?

Hi amybeth55,

My question is "why are you flying into Venice, then flying right off to Naples?" Sounds like a too-good-to-be-true fare you found somewhere or are you flying out of Venice back to the states thinking that round trip vs multi-city flight was best?

IMHO, your original plan is a potential disaster in the making, esp since you say that $$ is of minor concern. What is your overall travel plan? Are you going back to Venice? I would think you might want to stay a few nights in Venice then head down to Naples (train would be my option) but the trip to Naples/Sorrento from Venice will take all day no matter how you slice it.