From 10 January 2022, all passengers over the age of 12 must hold and present the "extended" Green Pass in order to board https://ambberlino.esteri.it/ambasciata_berlino/de/in_linea_con_utente/covid-19/misure-adottate-in-italia.html.
According to Legislative Decree No. 221 of 24 December 2021, FFP2 masks must be worn when travelling on all regional and interregional transport.
All information and FAQs can be found on the official website of the Italian government https://www.dgc.gov.it/web/ and here: https://ec.europa.eu/info/live-work-travel-eu/coronavirus-response/safe-covid-19-vaccines-europeans/eu-digital-covid-certificate_en
Please inform yourself here: https://www.dgc.gov.it/web/
Have your negative test result, proof of recovery or vaccination certificate in digital or paper form together with your ferry ticket and a valid identification document ready when boarding.