Rent a Car drop off in Venice

Sonja, There is only one location in Venice that is reachable by road, the Piazzale Roma at the end of the causeway from the mainland. This is directly across from Venice railway station and served by vaporetto. Searching for "car hire Piazzale Roma" will list all the usual companies.
The road dead-ends at Piazzale Roma, you either drop off your car, go into one of the paid parking buildings or double back to the mainland.
Other locations are on the mainland (Mestre) and require a bus or train to reach the Venetian islands.

And be SURE to go EXACTLY the speed limit - or even better, below the speed limit - on the causeway bridge from the mainland to Piazzale Roma. There are plenty of postings on this forum by people who got zapped by cameras on that bridge, and charged very high fines for going just 1 or 2 kms/hr over the speed limit.

Yes, and there are three speed cameras and we have heard from people who got a separate ticket from each one.

I don’t think the Autovelox speed cameras are programmed to issue tickets if you drive above the speed limit by less than 5 km/h. Nevertheless stay within the speed limit.