The Assault Vest only prevents the Pokémon from choosing status moves, not from using them. If a Pokémon has selected a status move to use, but obtains an Assault Vest before executing the move, the move can still be executed successfully. A Pokémon holding an Assault Vest can still use status moves via Instruct or Dancer.
In Pokémon UNITE, the Assault Vest is a held item that grants the user shield against Sp. Attack damage after leaving combat and increases their HP and Sp. Defense. After 5s out of combat, the user receives a shield equal to 9/12/15% of max HP, at grades 1, 10, and 20 respectively; this effect does not apply if the user has an existing Assault Vest shield. HP and Sp. Defense is increased by 18 and 0 at Grade 1, and by 270 and 51 at Grade 30.
Assault Vest was introduced as an Pokémon Tool card in the Pokémon Trading Card Game during the Japanese XY BREAK Era. It was first released in the Japanese Red Flash expansion before debuting in English in the BREAKthrough expansion. When this Pokémon Tool card is attached to a Pokémon, any damage done to that Pokémon by attacks from an opponent's Pokémon that have any Special Energy attached to them is reduced by 40 (after applying Weakness and Resistance).