Game Freak has confirmed that items are in fact usable during Dynamax. For example, Dynamaxed Pokémon can use Life Orb just fine.

What doesnt work with Dynamax?

1 Answer. Held items that affect you which are disabled in dynamax are: Choice Band, Choice Scarf, Choice Specs, Gorilla Tactics, and Sheer Force temporarily stop working (including the stat boosts) if the holder is Dynamaxed. However, Assault Vest still works accordingly and prevents the holder from using Max Guard.

Does choice band work on dynamax?

When battling against Dynamax Pokémon, there are a few changes. ... In addition to that, when you have a Dynamaxed Pokémon, the effects of hold items including Choice Band, Choice Scarf and Choice Specs will stop working and Sheer Force does not power up the moves.