How do calendar invitations work?

There are a lot of factors that can change how calendar invites work. Usually for Apple stuff the calendar and the email are separate things so it doesn't work like Outlook and Exchange where you get an email invite that directly feeds into the calendar. Calendar invites usually appear directly in your calendar inbox in the calendar app.

Take a look at this article to see how it works.

If you are having trouble getting the invites from other people have the sender take a look at this article.

I am not positive if .ics files sent by email would bring along the sharing information with them. But this article seems to make it appear that they might?

I am sorry I don't have a clear answer for you, but hopefully these links can help you.

This makes more sense. Different services are not going to play nice together. You could add a Google calendar to your Apple Calendar application which might allow more functionality with those users.

https://support.google.com/calendar/answer/99358?hl=EN&ref_topic=10510645/

However it looks like according to this link that invitations only works with some types of calendar protocols.

"iCloud, Microsoft Exchange, and some CalDAV servers let you send and receive meeting invitations. (Not all calendar servers support every feature.)"

Google is CalDAV, but as the article says only some servers are supported. I have never really used invitations like you are talking about with Google users usually just Apple to Apple.

Have you considered using Outlook instead? It might better meet your needs. They have apps for both OSX and iOS. I use Outlook for all my work stuff and Apple Mail for my personal email.

From your first posting…

Start here: https://en.wikipedia.org/wiki/ICalendar

1: If it is a valid iCalendar ICS file attachment invite, yes.

2: Apple IDs are not relevant here, save that many are also email addresses.

“I have some issues” is true of us all, alas not something we can address without rather more detail.

From your second posting…

Add-on anti-malware apps, add-on security apps, add-on cleaner apps, add-on VPN apps, or other such apps, installed here? Those can and sometimes do get in the way, and in unexpected ways.

iCloud is not related to this issue, save that you can enable and create and use iCloud Calendars, which are stored in iCloud, in addition to local calendars.

How this message arrival works, in very rough terms:

1. Embedded ICS attachment arrives via mail
2. scanner in mail detects ICS, and parses it. Or it’s mis-formatted or gets mis-parsed, and 🤮
3. Mail passes the ICS info to Calendar
4. Calendar offers the invite.
5. You accept or decline, and an ICS file is generated and sent to the originator.

What seems to be the question…

Reading through all of what you’ve posted, it’s from step 5 onward that’s somehow messed up here; that the person that sends the invite is not receiving the response.

Have they checked their spam folder, and their message-processing rules, and their spam settings?

Do other folks from other mail providers also sending invites also not receive replies triggered by your invite responses?

There have been issues with receiving responses in some other mail and calendaring tools, too: https://answers.microsoft.com/en-us/outlook_com/forum/all/outlook-calendar-invite-no-response-required/546efb04-02af-4fec-8644-2cd805ac7c29

Which means you’re going to need to do some troubleshooting and some debugging, and try some different combinations with the sender. As this might well be the sender’s problem, not yours. Have them try the web calendaring interface, or some other tool (same as the earlier try-a-different-sender), for instance.