Before Catalina, I used the iCal widget in the Dashboard as a way to quickly view the calendar. But Apple removed it all together now. So I come to use the Calendar item in Notification Center. Currently, it only shows the upcoming events, not the calendar itself. Is there any way to change it? Or if there is some way to quickly show a calendar, please do tell me.
How it is:
How I want it to show:
Try Mini Calendar - once installed & launched, it becomes an option to add in Notification Center: https://apps.apple.com/us/app/mini-calendar/id1088779979?mt=12
You can also disable the menu icon etc..
On macOS Big Sur, the new design of the Up Next widget can now show a full calendar on M size.
Go to Notification Center by clicking on the Day time button on the Menu bar, click Edit Widgets and choose Up Next, choose size M and click the + icon. 
