I  found an aerial view of the new building from Esri. Together with my own image from December 2023 of the new ferry terminal https://commons.wikimedia.org/wiki/File:Terminal_de_ferry_Port-Maria,_Quiberon-41400.jpg I have refined the building. In fact there are 2 buildings combined with a big roof.

I keep the note open because there can be more finer tagging of the ways done.