Setting the default calendar in icloud

Using this reference,
(Scroll down to “Set your default Calendar”

I’ve set my iPhone, iPad and Mac so they all use my gmail calendar as the default calendar. I’m assuming that it makes good sense to have all of my devices to use the same default calendar.

When I got to the “On” section of the above web page,
I logged into but my Gmail calendar is not visible.

Even though I can add a new Calendar, there are no options to sync to my Gmail calendar (or any other new calendars).

I’m not sure why I need to set a default calendar in iCloud, since all of my other Apple devices are using my Gmail calendar as the default calendar.

I’m using my gmail calendar as my calendar reference, because I can access it across all of my devices and platforms. I use my Gmail calendar to add/delete ALL of my calendar events, which will hopefully get synced to all of my devices.

What do I do to add my gmail calendar data in iCloud?

I believe (I may be mistaken, though) that those directions are for iCloud calendars. The steps you followed on your devices still work for other accounts, but that wouldn’t translate to I don’t believe your Google calendars will show up in, so instead if you are on the web you’d want to log in to your Google account directly and use their web app for the calendar.