Dynamax Pokémon are also immune to Encore, Torment, and Instruct.

Can you use Encore on dynamax Pokémon?

A Pokémon affected by Encore can use a Z-Move even if it is locked into another move (including on the same turn it became affected by Encore). ... Encore fails if it targets a Dynamax Pokémon. Dynamax Pokémon that are affected by Encore (due to being inflicted with it before Dynamaxing) can use moves regardless of Encore.

What is the difference between Gigantamax and dynamax?

The Dynamax forms of Pokemon only make them bigger, but the Gigantamax forms of Pokemon not only make them bigger, but also completely change the appearance of the Pokemon.