Green tick doesn’t show when someone accepts my iPhone or Mac event on Calendar app

Hi

When I send an event invitation from my Mac, or iPhone, and someone accept, the green tick does not show i the event.

The only way to get the green tick to show it to open the email response on the Mac and clock on the attached .ICS file. This means I have to open every response email.

I have see a few similar discussions on this topic, but they are now closed without resolution.

I have the most current versions of IOS and MACOS BTW.

Does anyone have any ideas?

Thanks

Tony

[Re-Titled by Moderator]

Original Title: ical green ticks not showing