Hey Fmeng! Sorry to hear that, I know what it’s like to lose important data.
Did you use Notes on any other devices?
If you do have other accounts (Gmail, Yahoo, Aol, etc), if you look I’m a System Preferences > Internet Accounts, select other accounts besides iCloud, are “Notes” checked? If not, you can check them and see if they show up.
Same on iOS > Settings > Passwords and Accounts, can you check there?
I only ask because sometime people will be syncing with Notes (Or other data such as Contacts) with one account and think it’s syncing with another account, simply by “checking” “Notes” on the other account might bring them back, (Hopefully in your case).
Otherwise, I have another solution:
If you DID have notes on an iPhone before they deleted, and you DID have an iPhone backup from that time period:
Erase your phone, then choose the option to restore your backup, (Whether through iCloud or iTunes (Or Music, from your computer),
Once the backup has finished restoring, IMMEDIATELY place your iPhone/iPad in Airplane mode as soon as you see the home screen, (Just to ensure no internet connection).
THEN Check Notes app, if they are all there, (Which I’ve seen before), you can move them to the “On My iPhone” section to ensure they are saved,
THEN, Re-enable the Internet, most likely they’ll be gone from iCloud, but still accessible on your iPhone.
I’ve only had this work a handful of times but without another backup is probably the best shot.
You can do something similar with your Mac, including restoring a backup or restoring the database, but I know you didn’t have a Time Machine or another backup, which is why I mentioned using your iOS devices (If you even have any), and since restoring any archives from iCloud.com failed to restore any.
Anyhow I truly hope one of those suggestions helps! Otherwise apologize and recommend backing up, even having several different backups, you can get external hard drives with a large capacity from most big box stores now for pretty cheap, hope that helps!