Gmail calendar invites not recognized by Apple Calendar app and iCloud Calendar

I've been browsing the forums for about a week and haven't found any questions/answers which are similar to my exact issue. I've included a bunch of details regarding my current setup just in case something small is making a difference:

• My primary personal calendar is my iCloud calendar, and the app I use on all my devices is the default Calendar app.
• My partner's primary calendar is with Google Calendar, and he uses the Google Calendar app on his devices.
• His calendar is shared with me as a subscription (view only) which is stored under my iCloud account. He's in and out on appointments throughout the day, so this lets me know when he's available.
• My primary Apple ID is a me[.]com address, but I keep this private and only send/receive email through an iCloud alias.

With those details, the issue is when he invites me to an event, I receive an RSVP email from Google with two attachments ('Mail Attachment.ics' and 'invite.ics'). When I open either of these files, I get directed to the Calendar app which opens the event from his calendar that I'm subscribed to — I'm forced to manually create the event on my calendar which defeats the purpose of an invite.

I thought I remembered that several years ago the Calendar app/Siri would automatically detect these invites and allow me to RSVP within the Calendar app, and the RSVP status would be relayed back to my partner's Google calendar.

Is there something in this setup which is incorrect, or has anyone else with similar issues found a solution? I appreciate any help or insight anyone would be able to provide!

Thanks,

Will