I am looking for a book that has a spaceship with cities (including a "New London") as well as lakes and an artificial sun and stars. The ship starts to crack and the authorities try to hide that fact from the travelers.
Could this be The World Gives Way by Marissa Levien?
Imogene and Marcus Carlyle's penthouse in New London was a "three-story feat of opulence...an easy nonverbal reminder that they had secured a permanent place at the top of the food chain." As a honeymoon present, Marcus purchased Myrra Dal's maid contract. "In fifty years, Myrra would be free...the work contract her great-grandmother had signed would finally be fulfilled...Working for the Carlyles, she had more freedom then she'd had in the laundry or in factories. But there was still always the invisible leash...".
"Something was wrong with the world. The ship." Top scientists and physicists studying and charting the integrity of the ship's hull had determined that a widening crack was irreversible. Neither Imogene nor Marcus Carlyle wanted to witness the implosion of the ship. Myrra was asked to continue to care for baby Charlotte. Myrra refused to wait and only get what she would be given when her contract expired.