Reminders app: delete reminder that won't delete

I'm super tardy to the party, but for anyone possibly experiencing this currently and checking top Google results for a resolution, try the following: Move the "rogue" scheduled task to a new list (via "Add List" located at the bottom-left corner of your app window) or pre-existing list within your Reminders application. You can do this via access the pop-up menu that appears when right-clicking the task, and I'm assuming you can also drag and drop. From there, click the list to which the task was moved, and then proceed to downgrade priority or delete. Lastly, revel in your personal triumph.

If the problem is still there, try booting into the Safe Mode using your normal account. Disconnect all peripherals except those needed for the test. Shut down the computer and then power it back up after waiting 10 seconds. Immediately after hearing the startup chime, hold down the shift key and continue to hold it until the gray Apple icon and a progress bar appear. The boot up is significantly slower than normal. This will reset some caches, forces a directory check, and disables all startup and login items, among other things. When you reboot normally, the initial reboot may be slower than normal. If the system operates normally, there may be 3rd party applications which are causing a problem. Try deleting/disabling the third party applications after a restart by using the application un-installer. For each disable/delete, you will need to restart if you don't do them all at once.

Safe Mode

Can you select the reminder and then delete it with the delete key?

Do a backup.

Quit the application.

In Finder hold down the option/alt key while selecting the Go menu item. Select Library. Then go to Preferences/com.apple.reminders.plist. Move the .plist to your desktop.

Restart the computer, open the application and test. If it works okay, delete the plist from the desktop.

If you want to make your user library permanently visible, run the below command in Applications/Utilities/Terminal.

chflags nohidden ~/Library/

You are welcome. Are you looking in your user Library or the hard drive level Library?