Outlook acceptance of calendar invite not showing in calendar app, emailed ICS instead

"Is the account you're sending the invite to a standard Exchange account, or is it affiliated with a business or school?"

As I said, this issue occurs reliably when adding invitees from large corporations to an iCloud event. The invitee sees the typical iCloud invitation pictured in my post. How they respond, i.e. which of the two accept buttons they click, determines whether or not I will receive an only-slightly-useful email noting their response or the desired result of the invitation's acceptance actually appearing in the calendar event itself.

"Are you able to send invites to other Exchange accounts?"

My issue is not with sending invites, my issue IS that the invitee's response is not always visible in the calendar if they do not already know that they must click in the body of the invitation.

"Are you able to receive invites normally to the same accounts?"

Invites are received normally on my end. I do not know if my acceptance registers in their calendars or not.

"When you send an invite to a standard Exchange account or other accounts, is the invitee's response visible in your calendar?"

With respect, neither I nor the recipient has any way of knowing what flavor/version of Exchange (school, business, Exchange Server, Office/Microsoft 365, etc.) they are using but I CAN say that depending on which of the two accept buttons they click, determines whether the invitee's response is visible in the calendar.

"Is the account you're sending the invitations from, the same corporate account they are being received by?"

No. The invitations are generated by my iCloud calendar and sent (I sincerely hope) by the default email account on my Mac which is my Office365forBusiness account.