What does this mean? I have reminders set to open files in, say Numbers, but this notice keeps appearing?

This is part of the OS security system that prevents (potentially malicious) apps from opening files or applications on your system.

In this case it sounds like your notification is triggering (as you want), and it's trying to open the document, but the OS is blocking it (the app doesn't have authority to open documents).

The fix depends a little on exactly how you've setup the notifications to open a file - there's nothing in Reminders.app, so how have you set your system to (try to) open the file?

First question (which has already been asked) is what method are you using in your attempt to have the calendar (or Reminders) open the file? Is it an AppleScript? Is it a shortcut made with the Shortcuts App? What is triggering it to open a file?

Second question is can the Calendar app open a Numbers file even if it had permission to do so? A numbers file does not sound like something the Calendar app can open. I think you need your script (or whatever) to tell the Numbers app to open the file.

I have no answer for you but it works fine here running Mac OS Monterey. I made no new system setting modifications, just whatever changes I have made over the years. Calendar is not on the list of apps allowed to control my computer or on the list of apps with file/folder access. I chose a filename similar to yours, just in case it was the apostrophes causing a problem. I tried putting the file in various folders on my computer and even on a network drive. I did not find a way to make it fail other than when I moved it into the trash, but the error was not the one you are getting.

Yes, I can replicate that "does not have permission" message here in macOS Sequoia 15.0.

I think this is the result of the continued trend toward tighter security in macOS. Most of us were probably not even aware you could set Calendar to mess around and open files on the Mac at a future date!

"calaccessd" is not readily accessible to the casual user.

I'm not sure how to give "calacessd" Full Disk Access or whatever it needs to do its thing here, or whether that is still possible in Sequoia.

This does not appear to be a Numbers-specific problem but maybe forum participants more familiar with the technical details of macOS will be able to point you in the right direction.

SG

Just guessing, but you may want to review

Settings > Privacy & Security > Allow the applications below to control your computer.

Adding Calendar may help.

SG