Staring in Day One 5.6 and macOS 11 Big Sur, widgets can now be enabled in the Notification Center. https://www.apple.com/macos/big-sur/features/
Open the Notification Center on Mac. You can click the date at the top- right of the screen to open this. Scroll to the bottom of the widgets to find the option to edit the list.
On This Day - Revisit photos from past years with the On This Day preview.
Daily Prompt - See the Daily Prompt throughout the day and answer when it’s convenient for you.
Streaks - Keep track of your recent journaling streak and jump straight to the Calendar View (small widget) or to the Today View (medium widget).
Today - Quickly see your most recent photos and location history to jump straight to the Today View to create a new entry.