ポケモン改造で世界的に有名なハッカーがポケモンのNAND破壊はデマだと証言
剣盾にシステムいじる権限は無いとのこと

http://www.nintendolife.com/news/2019/11/random_now_people_are_blaming_pokemon_sword_and_shield_for_bricked_consoles

Prolific Pokémon modder SciresM – the same person who managed to hack Omastar into the game – has responded to the rumours, calling them "bait" and "obviously false".
He also points out that, as games, Sword and Shield have no special access privileges and would not be permitted by the Switch OS to access the NAND:

https://i.imgur.com/eGq7W2r.jpg