If you are upgrading from the base game (v1.0.0) or an older NSP dump, here is exactly what the v1.2.0 update adds:
Because no new software patches have been pushed to the title in years, the definitive "complete" version of the game is . If your update file matches this version, you have access to the absolute maximum amount of content available. Major Features Included in the Last Big Update: ring fit adventure switch nsp update new