It seems like you are not seeing all your notes in the Notes app on your Mac, but you can see them all on your iPad and iPhone. I know it is nice to be able to have the same notes on all of your devices. I'll be happy to help with this.
What I'd like to have you do is to make sure that you have Notes checked in System Preferences > iCloud > Notes.
You can also go to Settings > Notes on your iOS devices and check under accounts to see which accounts you use with the Notes app. Then you can go to Systems Preferences > Internet Accounts on your Mac and see if any of your accounts listed there are also used for Notes but may not be checked. Then close out of the Notes app on the Mac and reopen.