Why is a Task not syncing over to my Google Calendar?

Take a look at your Task Type settings. Likely what is happening is that the Type of Task you've created is hidden from the calendar view.

unhide task type gif

To confirm this, Edit the Type that is assigned to the Task in question and uncheck the box next to "Hide from Calendar View?" Click +Save to make your change.

Remember, any tasks created through Record Scheduling will not sync to 3rd party calendars.