Heavy Slam is "blocked by the power of Dynamax" and Dynamaxed Pokémon can't use self-KOing moves. What other moves fail when they're used by or on Dynamaxed Pokémon?
Weight-based moves cannot be used against Dynamax Pokemon (PokemonTrainerLui), but a PP is still used (BountyHunterStev)
Has immunity to OHKO moves (DaWoblefet)
Entrainment and Skill Swap fail when used against Dynamax Pokemon, while Worry Seed, Simple Beam, Role Play, Gastro Acid, Trace, and Receiver succeed (DaWoblefet)
Instruct fails against Dynamaxed Pokemon (Worldie)
Also, moves that force switches fail too. https://replay.pokemonshowdown.com/gen8anythinggoes-1197340019 https://replay.pokemonshowdown.com/gen8anythinggoes-1197341402 https://replay.pokemonshowdown.com/gen8anythinggoes-1197341402
Source: https://www.smogon.com/forums/threads/sword-shield-battle-mechanics-research.3655528/
Dynamax Pokémon are immune to flinching. Fake Out can still damage a Dynamax Pokémon, but will have no secondary effect.
Dynamax Pokémon are unaffected by moves affected by weight (such as Low Kick and Heavy Slam), one-hit knockout moves, and Destiny Bond.
Moves and Abilities that replace the target's Ability with the user's (such as Skill Swap, Entrainment, and Wandering Spirit) have no effect on Dynamax Pokémon. However, moves that change or suppress the Dynamax Pokémon's Ability altogether (such as Gastro Acid and Worry Seed) still work.
Dynamax Pokémon cannot be switched out by the effects of moves that switch the target out (like Roar and Whirlwind). Circle Throw and Dragon Tail will still damage Dynamax Pokémon without switching it out. Red Card also fails to switch out a Dynamax Pokémon, but is still activated and consumed. Dynamax Pokémon can still be forced out by their own Abilities or items, such as Emergency Exit or an Eject Button. If a Dynamax Pokémon has Magic Bounce and is targeted by Parting Shot, the move will be reflected and force the Dynamax Pokémon to switch out (the owner of the Dynamax Pokémon is still able to choose the Pokémon that it is replaced with).
Dynamax Pokémon cannot be affected by Disable or Cursed Body. A Max Move or G-Max Move can still be used if its base move was disabled prior to Dynamax. Dynamax Pokémon are also immune to Encore, Torment, and Instruct. 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.
source Bold moves and abilities are the ones that were not already mentioned in the other answer.
