Salutations jwa_8204,
Let’s explore and further isolate the issue.
Do you use any VPN software on your Mac? If so, can you disable it, restart your Mac and test again?
Next, let’s check the calendar while booted to safe mode and see if the same error shows up. Use safe mode on your Mac
Start up in safe mode
Find out whether you're using a Mac with Apple silicon, then follow the appropriate steps.
If you're using a Mac with Apple silicon
1. Shut down your Mac.
2. Press and hold the power button on your Mac. As you continue to hold the power button, your Mac turns on and loads startup options. When you see Options, release the power button.
3. Select your startup disk. It's named Macintosh HD, unless you changed its name.
4. Press and hold the Shift key, then click the “Continue in Safe Mode” button below your startup disk.
5. Log in to your Mac. You might be asked to log in again.
If you're using an Intel-based Mac
If you're not using a Mac with Apple silicon, you're using an Intel-based Mac.
1. Turn on or restart your Mac, then immediately press and hold the Shift key as your Mac starts up.
2. Release the key when you see the login window, then log in to your Mac.
3. You might be asked to log in again. On either the first or second login window, you should see ”Safe Boot” in the upper-right corner of the window. If you can't start up in safe mode, make sure that your Mac isn't using a firmware password.
Thanks.