Times of Malta writes that " The government has not excluded the possibility of an immersed tunnel between Malta and Gozo even though this option was not listed in the request for proposals for the €300 million project."

https://timesofmalta.com/articles/view/immersed-tunnel-retained-as-option-for-300m-malta-gozo-channel-link.869824

There were 4 bidders for the tunnel construction. Please read 4 Bidders for the pre-qualification questionnaire for Malta-Gozo Tunnel : Heavyweights and Unknowns.