Once European cruising starts up again after being halted due to Covid, there will be some big changes. The Italian Ministry of Infrastructure & Sustainable Transport has put forth a ban on large cruise ships (over 40,000 gross tons) to sail into the city center of Venice city.
Instead, they will need to dock at Porto Marghera, an industrial port about 6 miles away from where they used to be able dock. (which was close to St Mark’s square)
Culture Minister Dario Franceschini tweeted that the cruise ship ban is a fair decision that has been long-awaited for years as it was a shock to visitors in Venice seeing cruise ships “hundreds of meters long and as tall as apartment buildings,” passing in front of St. Mark’s Square.
This decision has been brewing since 2019 when the 65,590 GT MSC Opera cruise ship went out-of-control and rammed into a dock & the Uniworld River Countess river cruise boat in the Canal, injuring five people. 

Here is a list of ships that Balcony Travel sells that are under 40,000 GT  (GT is the volume of all the ships enclosed spaces)

Azamara Journey, Pursuit, Quest                  30,277
Crystal Endeavor                                               19,800
Oceania Insignia, Nautica, Regatta, Sirena 30,277
Regent Seven Seas Navigator                        28,803
Ritz Carlton Evrima                                          26,500
Scenic Eclipse                                                    16,500
Seabourn Odyssey, Quest, Sojourn               32,346
Seabourn Venture                                             23,000
Sea Dream I and II                                              4,333
Silversea Silver Shadow, Whisper                 28,528
Silversea Silver Spirit                                       39,519
Silversea Silver Wind                                        17,235

For perspective, here is the information for a Royal Caribbean ship
Harmony of the Seas                                      228,081