3-part-timeline
16 December 2020: RECOMMENDATION FOR MARGHERA by the Government Giuseppe Conte: “Grandi navi” shall go to Marghera as temporary solution (“attracco temporaneo”), until the new port is available for them.
26 March 2021: CONCORDO – AGREEMENT FOR MARGHERA: The recommendation above was confirmed by the new Government Mario Draghi: The concordo (agreement, but not a law!) is mentioned on the government website:
01 April 2021: DECRETO LEGGE (DECREE ON COLLECTIONG IDEAS FOR THE NEW PORT OUTSIDE THE LAGOON) entering into effect on 01 April 2021:
„In order to reconcile cruise activities in the territory of Venice and its Lagoon in line with safeguarding the uniqueness and excellence of the cultural, landscape and environmental heritage of this territory, the Port Authority of the Northern Adriatic Sea, within sixty days from the entry into force of this legal provision, shall proceed with collecting ideas, divided into two phases, pursuant to article 156, paragraph 7, of decree no. 50, concerning the elaboration of concepts, proposals and technical and economic feasibility projects relating to the construction and management of port facilities outside the protected waters of the Venetian Lagoon to be used by passenger ships exceeding 40,000 tons, and by container ships used for transoceanic transport, taking into account the results of existing studies.“
See the original text of the decree here on page 8, Article 3:
The decree refers to holding the competitions as described in article 156 (7) of 18 April 2016:
So here we are – we’ve got a RECOMMENDATION, AGREEMENT FOR MARGHERA, AND A DECREE TO START COLLECTING IDEAS:
BUT – There’s no explicit law that the ships are currently, or will be banned from the Lagoon.
Of course, one can deduct that the grandi navi will be banned from the Lagoon as soon as the new port is ready, which I believe some newspapers have done.