So my uncle who totally works at Nintendo has told me that the true villain team for Sword & Shield is Team Dexit, whose goal is to get every single non-Galar Pokemon out of the Galar region. They are lead by a Boris Johnson look-alike, and Team Yell is an organization created by Team Dexit to distract the people of the Galar region from Team Dexit's activities and spread misinformation about the ramifications of deporting all non-Galarians. Marnie is unaware of the true nature of this apparent fan club of hers.
The player seeks out Zacian/Zamanzenta, Pokemon of legend said to be able to protect the Galar region from evil, and eventually catches them. The player then does battle with Boris Johnson, but is defeated by the unexpected and overwhelming power of Boris' Eternatus (rumored to be another legendary Pokemon of the Galar region).
After their defeat, the player learns that Zacian's/Zamanzenta's true purpose is to guide a hero to Milkshakenus, the only Pokemon with the power to stop Johnson and Eternatus. The player gains the aid of Milkshakenus, and with it, defeats Team Dexit once and for all in a climactic and dairy-filled fashion.
or so my uncle who totally works for Nintendo says