My Mac Calendar v11.0 in my 24 inch iMac/Monterey

Hello Jantje5,

Please check out this link, which outlines the available options for changing how the calendar is displayed, which may help: Change General preferences in Calendar on Mac

To make it easier to view what’s on the screen of your Mac, please check out this link, which has options and suggestions that may be helpful: Make it easier to see what’s on the screen of your Mac

"Change the appearance of the desktop on your Mac

• Make the desktop less transparent: Choose Apple menu  > System Preferences, click Accessibility , click Display, click Display, then select “Reduce transparency.” The transparent areas of the desktop and app windows become gray.
• Choose a desktop picture with fewer colors or shapes: Choose Apple menu > System Preferences, click Desktop & Screen Saver , click Desktop, browse through the picture folders on the left, then select a less busy picture or a solid color on the right.
• Make borders darker: Choose Apple menu > System Preferences, click Accessibility , click Display, click Display, then select “Increase contrast.” macOS automatically reduces transparency and makes the borders of buttons, boxes, and other items on the screen more visible.
• Use a dark appearance: Choose Apple menu > System Preferences, click General , then click the Dark appearance. You can change the accent and highlight colors.
• Invert colors: Choose Apple menu > System Preferences, click Accessibility , click Display, click Display, then select “Invert colors.” If you turn on Night Shift, “Invert colors” is automatically disabled.
• Make colors easier on your eyes at night: Use Night Shift to make the colors on the screen warmer. 
• Differentiate or tone down colors: Apply color filters or tint the entire screen.
• Make the pointer easier to see: Choose Apple menu > System Preferences, click Accessibility , click Display, then click Pointer. You can change the pointer’s size and color."

Thanks!