In the Notes app, you can easily search and filter your notes across folders using Smart Folders.
Go to the Notes app , scroll to the bottom, then tap Convert to Smart Folder.
When you convert a folder, its notes are moved to the Notes folder and tagged with the name of the Smart Folder.
Note: You can’t convert a shared folder, a folder with a subfolder, or a folder that contains locked notes.
Do either of the following:
In the folders list, tap Edit, then tap Organize your notes with tags on iPad