I suspect you have a theme running from the Samsung Theme Store!
You'll need to either go back to the Samsung stock theme or choose another theme that's more compatible. You could also let the theme developer know so that they may update their theme to be more compatible.
This is another similar thread with theme suggestions to use > Galaxy-S9-S9/Update-calander-issues.
Current Phone ~
Samsung Note 20 Ultra 5G SM-N9860_256Gb SnapDragon 865+
Samsung One Ui 3.1/ Android 11.