Side quests are the primary way to level up. Following the main story exclusively will eventually lead to a "level gate" where enemies are too tough.
An (Nintendo Submission Package) is the file format used by the Nintendo eShop to deliver games, updates, and DLC to the Switch console. Unlike the XCI format (which mimics a physical cartridge), NSPs are the standard for digital installations. The Importance of Updates (v1.0.x and beyond) cat quest ii rom nsp update switch game upd
Updates often resolve minor frame rate stutters or bugs found in the launch version. Side quests are the primary way to level up