Google Calendars in Outlook 365

I've recently bought the Office 365 subscription and have been trying to synchronize all Google calendars with the Outlook application. Found this official help https://support.microsoft.com/en-us/office/see-your-google-calendar-in-outlook-c1dab514-0ad4-4811-824a-7d02c5e77126, but I have each calendar manually.

Free Windows 10 Calendar app easily opens them all.

Internet is full of 3rd-party apps which do synchronization, but I cannot believe it couldn't be done without them.

I haven't found any docs or similar thread about the differences between Windows 10 Mail/Calendar app and Outlook for desktop.

However, based on my test, if I added a gmail account to Outlook even if I manually chosed the Google account type:

Outlook will still add this account with IMAP (I think it's by design):

As far as the windows 10 Mail/Calendar app, if we manually choose the Google account type, all calendars will show in the Calendar panel. However, there will be no calendars synchronized to Outlook if we add the gmail account via IMAP:

Therefore, if we use Outlook to add a gmail mailbox, Outlook will automatically use IMAP. As Roady said in the following thread, IMAP protocol itself doesn't support Calendars: Outlook 2016 - How do I add a Full-Function Calendar to IMAP Account?

It seems that you could only refer to the official docs to add the gmail calendars, maybe there is an add-in which can help you sync all the gmail calendars: Connect Gmail Calendar to Outlook