Resolved! "Generate Code" deletes 6 source files from an imported example (Nx_MQTT_Client) from ST's set. Manually replacing files temporarily fixes (until the next "Project->Generate Code".
I've a bunch of issues with STM32CubeIDE.To repeat the "Deleted Source Files" issue in STM32CubeIDE, running on a Mac M2 or Intel (not a Rosetta issue) under MacOS Ventura 13.x. STM32U5 board. Do the following:File->Import... General:Import STM32Cube...