The safest way to get this NSP is to using a Switch with CFW.
While v1.0.2 and v1.0.3 fixed day-one bugs, (and the subsequent v1.1.1 hotfix) was the major game changer. If you are still running the base NSP, you are missing out on the Daybreak epilogue. Pokemon Legends- Arceus Switch NSP UPDATE
If you are manually updating via a PC or Switch homebrew tool (like DBI or Tinwoo), pay attention to the file details: The safest way to get this NSP is to using a Switch with CFW
Players can meet Arceus in their dreams to take on a gauntlet of increasingly difficult battles. This mode tests your strength against legendary Pokémon and other powerful opponents in unique, multi-Pokémon scenarios. Path of Solitude and Tenacity: Pokemon Legends- Arceus Switch NSP UPDATE