Many of you remember this announcement regarding the ability to sync your Gmail/Google Calendar with Outlook. :

Google calendar sync will cease to function for Outlook on Aug 1, 2014.

"Important Announcement about Google Calendar Sync
Almost two years ago, we announced that we ended support for Google Calendar Sync. Starting on August 1, 2014, this app will no longer sync events between your Google Calendar and Microsoft Outlook Calendar."

Maybe you purchased apps to continue this service. Here is a free app that you can download for free (at least for now) that will let you sync calendar and contacts both ways.

https://www.howtogeek.com/225489/how-to-sync-your-google-calendar-with-outlook/

Also, for Mac users, Microsoft has begun inviting Mac users to try its new Google Calendar and Contacts support in Outlook 2016 by downloading and installing the application from its preview site.

Up until now, many of Outlook's more advanced email features have only been available to users with an Outlook.com, Office 365 or Exchange email address. This week's global rollout means anyone with a Gmail account can take advantage of several of Outlook's advanced features, including Focused Inbox and richer experiences for travel reservations and package deliveries.

https://www.macrumors.com/2017/04/13/outlook-mac-google-calendar-support-preview/