Functionality is great across Apple devices. I think they are really adamant about their lack of interest in making their platforms open to other OSs. You're r

Functionality is great across Apple devices. I think they are really adamant about their lack of interest in making their platforms open to other OSs. You're right on there not being an API, but... Both Notes and Reminders have a full AppleScript / JXA interface that Apple has maintained for years. Any LLM with shell access can read notes, create folders, add reminders, mark them complete, etc... + iCloud syncs everything out to iPhone/iPad/Watch/Vison/whatever-comes-next automatically.