How can I reduce the height of Date Boxes in Calendar Office 365

@Anne L McQuade said

the boxes with the days of the week are so tall

Is your problem similar to this one?
https://learn.microsoft.com/en-us/answers/questions/5840738/calendar-adjustment

My suggestion to that user was to try resetting the View: View -> View Settings -> [Reset Current View]. But they never reported back if that fixed it.

If this doesn't work for you, please add a comment to this Answer and paste a screen shot of the Day Of The Week row from your Calendar. Just the top. Don't include any event information.

Hello, are you mainly using Month view?

You cannot directly reduce the height of the day boxes in Outlook Classic because it follows zoom and Windows display scaling, so go to Calendar and lower the Zoom using the slider or Ctrl plus scroll down, then check Windows Settings, System, Display and slightly reduce Scale or Text size if it is set high, or switch to a different view like Schedule View to see more events, these steps will give you more space in the calendar.