Try this first
Look here, in this order
- Stop editing that note, so nothing older is written over.
- The Trash in the sidebar keeps notes, canvases and chats for 30 days.
- Search: ⇧⌘F searches notes, chats and files.
- Note history: ⇧⌘Y on a note shows its earlier versions.
- Backups, if you turned them on: Settings › Sync & storage › Backups.
- Upgraded from 0.10? Canto saved a copy of your notes from just before the update, in its data folder.