I upgraded my Pixel 3 phone yesterday and discovered that the date and weather functionality is messed up on the home screen and right now there's no fix available right now. Unlike the "at a glance" display in Android 11 which was side by side the "at a glance" feature in Android 12 stacks the date over the weather. Under Android 11 if you tapped the date it would open your calendar but it's broken in Android 12 if the weather function is also displayed. Turn the weather function off so it's not displayed and it works. The current work around is to turn the weather display off in 'at a glance" and go into the Google App, click weather at the top of the screen and then add the Google weather widget to your home screen.
Note however that if you leave the weather function on in "at a glance" it will show you the temperature for your current location however the display will not show you any weather details. If you search for a different city it will not show you any details for that new city. In addition, if you had a list of cities that you check weather on the list is missing in Android 12. However if you again go into the Google app and tap the weather icon at the top of the applet the weather details are shown however there's no list there either but the search feature does work if you type in the city name.
Note however that if you leave the weather function on in "at a glance" it will show you the temperature for your current location however the display will not show you any weather details. If you search for a different city it will not show you any details for that new city. In addition, if you had a list of cities that you check weather on the list is missing in Android 12. However if you again go into the Google app and tap the weather icon at the top of the applet the weather details are shown however there's no list there either but the search feature does work if you type in the city name.