It was certainly years ago, and I don't remember the details. I didn't know support had been dropped for it.

To do it required jumping through some sort of weird hoops where I configured Outlook to sync to some sort of publicly-visible web calendar (it might have been an early version of what became Office365 later), and then I had to configure Google to "consume" that calendar.

It was really house-of-cards-y and I wasn't surprised when it fell down.