Navigate to the Google Calendar App on your Apps Launcher:
Look for a button near the top right corner (between Agenda and More buttons) that says Use New Calendar.
If you already have the Calendar open, refresh the page to get the button to appear.
Click on the Upgrade now button:
Click "Learn more about the new design" to get an overview of the new features in Calendar:
The new Google Calendar is cleaner, has more white space and is easier to read.
Partially reposted from: https://www.cnet.com/how-to/how-to-get-the-new-google-calendar-on-the-web-right-now/