This. Turning sync off shouldn't delete notes from iCloud. It just doesn't sync the notes from iCloud to the specific device in question so they are not visible

This. Turning sync off shouldn't delete notes from iCloud. It just doesn't sync the notes from iCloud to the specific device in question so they are not visible from that device. To confirm OP could have logged in icloud.com from browser and seen the notes there. Then you can decide on a per-device basis whether you want to sync notes and have them be visible on that specific device.