In Settings > Accounts, you can sync Google Calendars via Gmail or Exchange. The Gmail method is easier and is currently working but the major downside being it doesn't support push so more battery intensive and won't show calendar changes right away which for some may not be an issue for others it can be a major one.
For paying gmail customers, you can like always use the "Exchange" connection to sync your mail, contacts and calendars and have changes pushed instantly.
However, in iOS 13 Beta 2 all calendars do not sync.
On Google Calendar website, I have my main calendar "Work" but also two other "My Calendars", one is "Personal" one is "Family". Also have a a couple subscribed calendars. In iOS 13 Settings > Account, it shows the main calendar Work, and the subscribed calendars but not "Personal" and "Family".
The first thing I checked which for 99% of people with the issue is to go to https://calendar.google.com/calendar/syncselect and make sure all calendars are checked off. However, in my case all already are checked off. I tried unchecking rechecking, etc. On my Phone tried restarting, tried deleting the account and readding, no change. Even eventually did a fresh install of iOS 13 (without an iCloud restore) and issue persists.
Reached out to Google support. Didn't menion on iOS 13 since they would say they cannot provide support for beta software, but they spent a couple days and show no issue on their end and said to try another device.
Filed a radar of course already, but mentioning here to see if someone can confirm if they can replicate it, and or if they have found any way to fix it. I tried other things such as creating a new test calendar on the google calendar website but no luck Tried making calendar public in organization and toggling that setting but no change. To note, they all show up in Google Calendar app for iOS but that doesn't relay on the iOS accounts feature which is what appears to have a bug.
