My O365 displays my Google calendars just fine.
My iOS and macOS calendar apps display both just fine.
I use a handful of Google calendars, but almost never use the Google calendar UI directly and interact almost exclusively via the Apple or Microsoft UIs to the Google store of data. (As in I might use the Google UI directly perhaps once a year, and that's generally only to get the access/path to the iCal interoperability URL.)
I use a handful of Google calendars, but almost never use the Google calendar UI directly and interact almost exclusively via the Apple or Microsoft UIs to the Google store of data. (As in I might use the Google UI directly perhaps once a year, and that's generally only to get the access/path to the iCal interoperability URL.)