The Pokémon Global Link service will be closing after 9 years. As of February 24th, 2020 you will no longer be able to use any gameplay features that require a connection to the PGL on your Pokémon Ultra Sun, Pokémon Ultra Moon, Pokémon Sun, or Pokémon Moon games. That said, players will still be able to use other online functionality of the titles apart from the PGL.
Pokémon Sword and Pokémon Shield will also have similar features as to what was on offer through PGL, which will be available through the Nintendo Switch.