sleeper rail

There aren't any. The night train from Paris to Venice was cancelled when the pandemic hit and it doesn't look like it will return. But there are direct day trains from Paris to Milan.

Although there are other night trains you can use on the route. https://www.seat61.com/trains-and-routes/paris-to-venice-by-train.htm

The night train option involves a TGV to Stuttgart departing just before 6 pm. This train gets to Stuttgart just after the night train to Venice has departed, but you can catch an ICE train to Augsburg that passes it on the way, so you can board the night train in Augsburg.

Personally, I'd take the Freccia that departs just after 3 pm to Milan arriving about 10 pm and sleep in a real hotel room that does not shake and stop and start every hour throughout the night.

Very few people take the train that far. The Alps are a physical barrier too.

I suggest you fly on EasyJet from De Gaulle Airport to Milan Malpensa. They also fly from De Gaulle and Orly airports in Paris into Venice's Marco Polo Airport.

Flying is so much cheaper too.