Calendar not fully syncing between iOS 18 and MaOS Sequoia

I've an iPhone 16 Pro and Macbook Pro M4. I have noticed that, though my iCloud settings appear to be correct on both devices, not all of my calendar entries are being reflected on my Mac.

In iOS, I have iCloud Calendar, Reminders, Contacts, ... enabled. On MacOS the same adjunct is enabled.

One entry that is not showing up is under Gmail. So I changed the calendar to my iCloud email address and my "Home" calendar, then it showed up.

Now, this hasn't happened before and I am wondering why the accounts I have enabled under iOS aren't showing up in MacOS -- as I would believe they should. Sounds almost like a keychain issue?

I believe this is resolved by going in manually and adding the accounts on MacOS. But, this kinda bypasses the idea that iCloud might be syncing this data from iOS -- and I'm not sure whether these accounts apply here.

Pointers appreciated.