If your Google calendar can't be synced with the Windows Calendar app, there's a workaround. If you have an Outlook.com account, you can move your Google calendar events to your Outlook.com calendar and then connect
Outlook.com to the Calendar app.
If you don't have an Outlook.com account, you can sign up for one.
Sign in to your Google account and export the Google calendars you want.
Follow the on-screen instructions to save the file created when you exported your Google calendars to your PC.
Unzip (extract) the file—open the .zip file, tap or click Extract, and then tap or click Extract all.
Sign in to Outlook.com and go to your calendar.
Tap or click Import, and then choose whether you want to import events into your existing Outlook.com calendar or a new one.
Tap or click Browse, tap or click the .ics file that you unzipped, and then tap or click Import. If you exported more than one Google calendar, repeat this step for all the associated ICS files.
If you’ve already connected your Outlook.com calendar to the Calendar app, open the Calendar app and after a few moments, your Google events will appear.
If not, here’s how to do it:
Open the Calendar app.
Swipe in from the right edge of the screen, and then tap Settings.(If you're using a mouse, point to the lower-right corner of the screen, move the mouse pointer up, and then click Settings.)
Tap or click Accounts.
Tap or click Add an account, tap or click Outlook.com, and then follow the on-screen instructions.
Once you move your events from Google to Outlook.com, to continue receiving new events sent to your Gmail account or updates to older events that other people have created, tell people to send events to your Outlook.com email address.
If you shared your Google calendar, you'll also need to share your Outlook.com calendar.