Rhythm games require low latency. In Dolphin, ensure that is enabled to prevent screen tearing, but if you notice input lag, try disabling it. Additionally, using a wired controller can reduce lag compared to wireless. Tips for Mastering the Rhythm
You can map the Wii Remote's A and B buttons to a standard keyboard, Xbox controller, PlayStation DualSense, or arcade rhythm controller. Rhythm Heaven Fever Wii Iso