Yes, it can terastalize into its stellar type, but its terastalization works a bit differently. It transforms into the stellar Tera type (added in the indigo disk) but unlike other stellar types, it never loses its stab on every type, it also has a different form and has boosts to its base stat total (mainly its hp) taking it from a bst of 600 to 700. I’m not sure if it’s true but I think I heard that its signature move only becomes spread when it terastalizes.
Source: experience, this site, and that added bit I don’t know where.