If you are recently unable to copy messages in Outlook from Christmas 2023 and you get this error when attempting to copy meetings, which is "Copy Meeting is not supported"
It would appear Microsoft have determined that, and I quote "Actions related to copied meetings yield unexpected results, so we recommend avoiding copying meeting" this was made live as of build version 2311 (Build 17029.20000)
If you need to re-enable this "copying of meetings" then you can apply the workaround which is to navigate to the registry location, however if you receive a profile reset or rebuild you will need to get this set again!
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Options\Calendar
Then you need to create the registry key with Outlook closed and quit:
Name : EnableMeetingCopy
Type : REG_DWORD
Value: 1
That should look like this:
Then start up Outlook again for the functionality back.