To respond to the question about route and possible overnight stops, I have the same answer as NickB—-take the Gotthard Panorama Express from Luzern to Lugano by lake boat and train. From Lugano it is a simple journey to Venice (or elsewhere) by train via Milan.
The logical (to me, anyway) places to overnight on this route from Lauterbrunnen would be Luzern and Lugano, because you will be changing trains in these places anyway, and they are lovely lakeside places to stay on the nights of June 2 and June 3. Or if you would like to go further than Luzern the first day to shorten the following day’s journey time, you could take the lake boat as far as Vitznau, a small lakeside resort community with a good assortment of very nice small hotels. Check into one and leave your luggage, then ride the cogwheel train up to Rigi Kaltbad for a nice hike on trails well above the lake, with beautiful views. Next day catch a morning lake boat that gets you to Fluelen for the (once daily) departure of the Gotthard Panorama Express train to Lugano.
What is the name of your cruise ship? Some of the small ships are still using the cruise terminal at Venice, I believe. But If it turns out your cruise ship is actually departing from Ravenna, you will have a slightly longer train journey on June 4 to reach your port than you would going to Venice, but not too much. Or it is possible you will be picked up in Venice by the cruise ship line and transported to Ravenna by bus. have also read of at least one cruise ship that will stop at Trieste instead of Venice, so you will want to get this sorted out soon.
Here is a list I have found of the 10 cruise ships that are still scheduled to actually port at Venice in 2022:
https://www.cruisemapper.com/ports/venice-port-79
They are “small” ships, under the size limit banned from the Giudecca Canal and the Venice cruise port.