How do I fix Notes app causing lag on MacBook Pro M4 Pro running macOS Sequoia 15.3.1?

Notes.app is baked into the macOS, there is no stand alone application independent of reinstall a fresh copy of the OS.

relaunch the Notes.app holding down the Shift key and compare your results.

No resolve try a Safe Boot

A SafeBoot Start up your Mac in safe mode - Apple Support will sort many anomalies

Does a quick disk repair before it fully boots up, and certain system caches get cleared and rebuilt, third party system modifications and system accelerations are disabled temporarily.

Login and test. Reboot as normal and test. Caches get rebuilt automatically.

mattyu5 wrote:

Thanks for the advice! I've tried the safe mode to test it out, and I found out it was my "external mouse" causing the problem. It was not an issue while using the MBP trackpad, so I might consider getting a new mouse.

Good computing mattyu5 !