PrimeVue uses the system as the default darkModeSelector in theme configuration. If you have a dark mode switch in your application, set the darkModeSelector to the selector you utilize such as .my-app-dark so that PrimeVue can fit in seamlessly with your light-dark toggle.
An example implementation of a dark mode switch, you may extend it further by involving prefers-color-scheme to keep it from the system initially and localStorage to make it stateful. See this article for more information.