How do I recover missing OneNote files in the Notes app on iPhone?

Re: LOST 1 NOTE on my iPhone notes app! . . help!

If you haven't seen it slready:

Apple support's online article:If you're missing notes on your iPhone, iPad, or iPod touch - Apple Support

Eg: says:

"First, update all of your devices to the latest version of iOS, iPadOS or macOS to make sure the issue isn’t related to previous software."

Re: " I checked recently deleted but no folder of that sort existed or was visible."

Wondering just where you checked:

Eg:: "Check your Recently Deleted folder

If you store your notes on iCloud, check your Recently Deleted folder:

1. Open Notes, then tap the back icon until you see your Folders list.
2. Tap Recently Deleted and search for your note.

If you find your note in Recently Deleted or in another folder, you can move it:

1. In the Notes list, tap Edit.
2. Select the note that you want to move.
3. Tap Move, then select the folder you want to move it to."

________

If needed: the linked article at the top also has other suggestions, and tips for carrying them out::

Eg: "Check your account settings : If you store your notes with a third-party account or email service, like Gmail or Yahoo, check your settings"

and

How to: "Use Search (in Notes) to find your notes"