https://www.gamespot.com/articles/pokemon-go-first-october-community-day-details-rev/1100-6462077/

Now that September's Pokemon Go Community Day is behind us, Niantic has shared the first details on next month's event. October's Community Day is scheduled to take place on Sunday, October 21, and this time, the featured Pokemon will be Beldum, the first form of the powerful Steel/Psychic-type Metagross.

All throughout the event, Beldum will appear much more frequently in the wild than normal. Based on past Community Days, it is also likely that fans will have their first chance to catch a Shiny Beldum; while Niantic hasn't confirmed this, the developer has introduced Shiny variants of nearly every featured Pokemon during previous events, which all but guarantees that Shiny Beldum will make its debut next month.