It looks like you're referencing a — specifically the one that added Cindered Shadows (Wave 4 of the Expansion Pass) plus quality-of-life features like the Journal and extra save slots.
To update Fire Emblem: Three Houses to version 1.2.0, follow these steps: fire emblem three houses nspupdate 120 2 new
If you are playing on Steam Deck or a mid-range PC, the 1.2.0 NSP is essential. It looks like you're referencing a — specifically
Here are the detailed patch notes for update 1.2.0: fire emblem three houses nspupdate 120 2 new
When a user applies this NSP update, the console's system archives replace the older game files with the newer v1.2.0 files. This is cumulative, meaning v1.2.0 contains all previous bug fixes from v1.1.0 and v1.0.1.
: New quests, paralogues, and tea party interactions. Free Content Updates (For All Players)