Hi tet96,
If you'd like to recover a missing note, these steps might help.
It looks like you've had the chance to review If you're missing notes on your iPhone, iPad, or iPod touch, but let's double-check the information in that link.
Use Search to find your notes
1. Open Notes, then tap the back icon until you see your list of notes.
2. Tap the Search bar and type a word, phrase, or the title from the note that you're looking for.
3. Make sure All Accounts is selected. Search will check all of your notes in each folder across your accounts, like an email account.
If the issue remains after following those steps, let the community know which account your note was on.
We hope that helps with your question and take care!