If you don't want a specific project to show on your calendar, you have two options.

If you want to hide it for yourself only, go to your Google Calendar. On the calendars list on the left side, hover over the name of the project you wish to remove and click on the X next to it, this way you will remove the project from the calendar, you can also just un-check it to hide it.

If you are the owner of the project or an admin, go to the Marketplace tab, look for the Calendar plug-in, select it and click Deactivate, this will deactivate the calendar for all the team members of your project.

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