SnipNotes is designed for managing lots of notes and provides several helpful organization tools for this purpose.
Overview
Categories are like folders on your computer. You can group your notes by topics and create your own organization system. Every category can be assigned an icon for quick recognition.
You can access categories in several places of the app:
In the app: On iPhone and small iPads, tap the "Categories" button in the upper left corner to reveal your categories. On large iPads and on macOS, categories are visible by default

In the category widget: Long-press a widget to edit it and select a different category to show your notes (iOS only)
On Apple Watch: Tap on “View notes” and swipe left or right to browse through your categories. You have to enable synchronization for each category on your iPhone first: Swipe left on a category and turn on the switch “Synchronize with Apple Watch?”
To move a note into another category:
Alternatively, you can also use drag and drop to move notes between categories.
See the separate article on Note Tags