https://www.techradar.com/news/pokemon-go-wont-connect-to-your-apple-watch-after-july

Niantic has announced it is officially pulling support for Pokémon Go on Apple Watch devices. 

In a Niantic Support post titled 'Discontinued support for Apple Watch', the developer revealed it is ending Pokémon Go support on Apple Watches on July 1, 2019.  From this date on, you won't be able to connect the game to your device.