Gmail calendar invite notifications not appearing in iOS native Calendars app inbox

Hi all, wanted to start a discussion about an issue I've been experiencing now for a while which I've been unable to resolve.

I've recently moved to a new company who uses Gmail for business and I've been experiencing compatibility issues with the iOS native Calendars app and Gmail, specifically surrounding the invitations inbox.

Put as simply as possible, calendar invites sent to my work Gmail address do not show in the Calendars inbox on my iPhone and therefore I am not given the opportunity to accept or decline. The events themselves automatically appear as tentatively accepted at their respective date/time in the Gmail calendar itself, and if I open these entries, only then am I given the options to accept or decline. Initially, for the first month or so, everything was working perfectly and I did not have this issue - it suddenly began occurring without rhyme nor reason.

My MacBook Pro receives the calendar inbox notifications for Gmail faultlessly, and I can accept/decline them as I wish. Weirder still, my Apple Watch (non-cellular), which supposedly only "mirrors" my iPhone notifications also shows the inbox notifications!

Some background information:

- All my devices have the Gmail account setup using the "Google" quick-add method within "Accounts & Passwords"

- All Google services/apps are working as normal, there are no notification issues there

I have taken the following steps to resolve the issue, none of which have worked:

- There are some fairly odd/unusual notification settings within Gmail, which require some tweaking to ensure that they work correctly with the native Apple Calendars applications. I have played with each and every possible combination, to no avail

- iPhone has been fully DFU restored to factory settings and setup from scratch, again to no avail

- Accounts have been removed/re-added from all relevant devices, again, no joy

I wish I could accept this as being a 'compatibility issue' and leave it, but I'm loathed to use non-native iOS apps to access my calendar as they're all just dreadful, plus it was working fine before, so why isn't it working now?

If anyone has experienced the same or has any advice whatsoever, I would majorly appreciate the assistance. My calendar is absolutely vital for my work and not receiving invitations into my native iOS Calendars inbox is causing me a major headache.