The official Pokémon website has announced that Gigantamax Butterfree and Gigantamax Garbodor will be available in Max Raid Battles until November 30th, 2020 at 3:59 p.m. PST.

Gigantamax Butterfree and Gigantamax Garbodor in Max Raid Battles in November

Explore Galar’s dens to discover loads of Bug-type and Poison-type Pokémon.

A brood of Bug-type and Poison-type Pokémon have begun lurking in Pokémon Dens all over the Galar region in Pokémon Sword and Pokémon Shield. Through November 30 at 3:59 p.m. PST, encounter the Bug-type Pokémon Butterfree, Shuckle, and Ninjask, along with the Poison-type Pokémon Vileplume, Toxicroak, and Garbodor, more frequently in Max Raid Battles. Plus, Gigantamax Butterfree and Gigantamax Garbodor will appear more often. Note that this event does not affect the Pokémon encountered in Dynamax Adventures.

Source: https://www.pokemon.com/us/pokemon-news/gigantamax-butterfree-and-gigantamax-garbodor-in-max-raid-battles-in-november/