Notes app creates files, how do I add to backup?

The Notes app can be synced with iCloud and backed up. Go to Settings>Press your name at the top>iCloud and enable Notes

This Will now sync across your devices and backup your data to the cloud.

Should you choose to house your notes in iCloud (which is very different from backing them up), you would be provided a “Recently Deleted” folder in Notes which contains notes deleted within the past thirty days.

Aside from that, you would have to rely on the place you house your notes (e.g., Outlook) to serve as the backup mechanism.