2010 MacBook Pro on Mavericks, Notes are not syncing with Notes on iPhone 5s on ios10. Is there a compatibility problem? I have tried all the usual remedies without success.
Yes, there's a compatibility problem. Notes were upgraded in iOS 9 and OS X El Capitan, and you can't sync between OS versions from before and after the upgrade. You'll need to upgrade your Mac to El Capitan or Sierra (which you should do anyway, since Mavericks will soon stop getting security fixes, if it hasn't already).
As a workaround, you can use a web browser to access notes in the cloud via web app. It’s not as convenient as the native app, but you can get at the notes from https://icloud.com
Use Fluid to create a fake Notes App
Following @Mike Scott suggestion of using a web browser to manage the Notes in your iCloud account, I would recommend using Fluid to create a fake Notes App.
This is how I am doing right now in my very old MacBook while I wait for the arrangement of my Mac. In fact, I really enjoyed this method so much that I also created a Fluid App for the Reminders.
- Download here the last version of Fluid compatible with Mavericks.
- Install as usual and launch the application.
- In the URL field introduce this: https://icloud.com/#notes2
- In the Name Field introduce, for example, "Notes (Fluid)".
- Create the App.
Optional but handy
- Start the app "Notes (Fluid)" and open its Preferences.
- Under "General" change the App icon: browse for some image, or better, just select the built-in Notes App.
- Under "Behavior" ensure "only hides the windows" is selected.
You can use this Fluid App like a browser; thus you can create new tabs to manage a different notes in the same Window.
Don't sync the Notes app with iCloud, use a different service instead!
When I first downgraded to Mavericks, I had been using iCloud to sync Notes for a couple of years, and I also discovered I could no longer keep Notes in sync between my Mac and my iPhone.
So, I migrated to syncing Notes with my Google account. Now the Notes app on my Mavericks Mac and my iPhone (running iOS 12 atm) sync without problems!