Somethings have suddenly gone missing in widgets & settings...

It sounds like something unexpected happened with the system settings or file structure on your MacBook, causing the Notes and Reminders (and potentially other apps or features) to go missing. Since you didn't manually remove or uninstall these, it could be related to an update, system glitch, or corruption. Here are some things you can do to troubleshoot and potentially fix the issue:

• Sometimes, apps or features might just be hidden or disabled rather than completely removed.
• Go to System Preferences > Extensions or Notifications & Focus to see if Notes and Reminders are still listed but turned off or hidden.

• Press Cmd + Space to bring up Spotlight and type "Notes" or "Reminders" to see if the apps are still installed but just not showing up where you expect.
• If found, try opening them directly from Spotlight.

• You mentioned that the widgets are stored in /System/Library/CoreServices, but for Notes and Reminders, you can manually check their respective locations:
  • Notes app: It’s usually found under /Applications/Notes.app.
  • Reminders app: Similarly, check /Applications/Reminders.app.
  • If they are missing, you might have a deeper issue or possible corruption with the system files.

• Reboot in Safe Mode: Restart your Mac and hold down the Shift key during boot to enter Safe Mode. Safe Mode can help repair file system issues and clear certain caches that might be causing problems.
  • Once in Safe Mode, check if Notes and Reminders appear. Restart normally to exit Safe Mode.
• Disk Utility: Open Disk Utility and run First Aid on your startup disk to check and repair any potential file system errors.

• Since Notes and Reminders are system apps, you can't easily reinstall them like third-party apps. However, you can try to restore macOS using the built-in recovery options without erasing your data:
  • Restart your Mac and hold down Cmd + R to enter macOS Recovery.
  • Select Reinstall macOS from the options. This will reinstall macOS over your current installation, potentially restoring any missing system apps without deleting your data.

• Even though you’re on the last supported version of macOS for your system, it’s worth checking if there are any minor updates or patches for macOS Monterey 12.7.6 that could fix issues like this. Go to System Preferences > Software Update to make sure everything is up to date.

• To see if the issue is specific to your user account, you can create a new user account:
  • Go to System Preferences > Users & Groups > + to create a new account.
  • Log into the new account and check if Notes and Reminders are available. If they are, there may be an issue with your original user profile.

• Open the Console app (Applications > Utilities > Console) to check the logs for any error messages or unusual activity related to Notes or Reminders that could point to the root cause of the problem.

• If all else fails and nothing seems to resolve the issue, you might want to back up your data and perform a clean reinstallation of macOS Monterey. This would essentially give you a fresh start with the last supported version and should restore missing apps like Notes and Reminders.