Cannot Open .ics files in iCal or Outlook for Mac OS

I have Mac OS v 11.6 (updated a couple of days ago) and I am using iCal v 11.0. I click on a downloaded appointment (.ics file type) and get an error message that cannot open file. The same thing happens in MS Outlook for Mac v 16.53(21091200), although the error message is cannot import file. There was a similar quest asked for Mac OS Mojave that said to try creating a new calendar and import the appointment through File>Import. I tried that, and I did not get an error message. Instead, I got nothing. No appointment in iCal--nada.