Reminders app won't sync on macOS Monterey, remaining blank and unresponsive

Question

I have a problem with the Reminders app on my iMac that after upgrading to a 2TB SSD, installing the latest version of Monterey and using a Time Machine backup to restore my files. The problem I am having is as follows:

1. The Reminders app remains blank and does not sync any lists or any reminders.
2. The lists or reminder fields do not appear on this particular iMac despite the fact that Reminders syncs without any problems on other Macs and iPhone I own and that the iCloud copy also syncs correctly with these other devices.
3. I am not able to add or remove any lists (or reminders for that matter) as the button to add a list does not work when I click on it.

I contacted Apple Support and they told me to:

1. Turn off and on reminders using my AppleID on System Preferences and restart my computer, but that did not help.
2. Remove the caches on the Library folder but that did not help.
3. Reinstall macOS Monterey but that did not help either; and finally
4. Create another user account and transfer all my data to this new user, which I know it will work (as I tried it with Apple Support successfully); however, this means I will lose all the configurations from my other apps and macOS and I will have to recreate a very complex user account from scratch, which is quite a bummer.

I tried to follow other suggestions on this and other websites, but they either did not work or were outdated. Is there any way to solve this problem?

Answer 1

After trying many things that Apple Support and this and other websites recommended without success, I decided to do the following:

1. Quit Reminders.
2. Go to ~/Library/Reminders/
3. Remove all folders from this folder
4. Restart Reminders.

However, this did not work. I was stuck with the same problem. Still no syncing and the app remained unresponsive. I decided to pray about it and I got inspired, or so it seems and then did the following:

1. Launch Activity Monitor on the /Applications/Utilities folder.
2. Search for remindd, the Reminders background app, and make it Quit in Activity Monitor by selecting on the list view and click on the button with a cross. (These two steps might not be needed but I think it might be important to avoid any database corruption due to a sudden sync event while you are doing the following steps).
3. Go to ~/Library/Reminders/
4. However, do not remove the folders MLModels and Stores; first make a backup of them by copying them to the Desktop or whatever place you'd like.
5. Make these folders empty by sending their contents (and not these folders themselves) to the trash by means of Command + Backspace or by dragging their contents to the trash.
6. Relaunch the Reminders app and voilá, you should have all your reminders back.