Hi there! I understand you're having trouble opening all your notes in the Mini Notes app on your Mac running OS X 10.15.7. Let's see if we can get this sorted out for you.

To start, could you tell me a bit more about the issue? For example:
- Are some notes opening while others don't, or can you not open any notes at all?
- Is the app itself opening but just not displaying notes?
- Have you noticed if the problem started recently, maybe after an update?
- Are your notes synced via an account like iCloud or another service?

Meanwhile, here are some initial steps we can try:

1. Restart the Mini Notes app: Quit the app completely (right-click its icon in the Dock, then choose "Quit"), then reopen it. This can clear temporary glitches.

2. Restart your Mac: Sometimes a simple reboot can resolve issues by clearing system-level hiccups.

3. Check your account syncing settings: If your notes are linked to an account (like iCloud), open System Preferences > Internet Accounts, and make sure Notes syncing is enabled for your account.

4. Check Folders View: In the Mini Notes app, try switching to the Folders view to see if your notes are organized there but not showing up on the main screen.

If these basic steps don’t resolve it, we can explore more advanced options such as resetting the app's plist file or logging out and back into your syncing account to refresh connectivity.

Let me know what you observe with these first steps and if you can share more about the problem! That will help me guide you better.