Apple Support has posted a helpful guide to Apple Weather especially for people coming from Dark Sky:
Dark Sky’s features have been integrated into Apple Weather. Apple Weather offers hyperlocal forecasts for your current location, including next-hour precipitation, hourly forecasts for the next 10 days, high-resolution radar, and notifications.
Apple Weather is available on devices running iOS 16, iPadOS 16, and macOS 13 Ventura. If you’re new to Apple Weather, here are some tips to get started.
The background, in case you are wondering and don’t already know, is that Apple bought Dark Sky a while back, and now they have shut down that service.