Riker's Luna-class command from 2379, which later became the Titan-A and was renamed Enterprise-G in Picard.
The USS Titan is a Luna-class Starfleet ship. William Riker took command of it at the end of Star Trek: Nemesis in 2379, after many years as first officer of the Enterprise-D and Enterprise-E, and Deanna Troi joined him aboard.
The Titan appears in Lower Decks, where Captain Riker brings it to the aid of the USS Cerritos, and it returns in later episodes of that series. The ship's crew is drawn from many species, in keeping with its mission of exploration.
In the third season of Picard, set in 2401, the ship is the USS Titan-A under Captain Liam Shaw, with Seven of Nine as first officer. Picard and Riker take it on an unauthorised mission to help Beverly Crusher, which pulls the ship into a conflict with the changeling Vadic and the Borg. At the end of the season, the Titan-A is renamed USS Enterprise, NCC-1701-G, under Captain Seven of Nine.