Hi, there is no Joom Calendar. If I look your printscreens, You mean JEM Joomlaeventmanager.
You can try with the official joomla templates, there it will work best. If an other template creates problems, it is up to them to help. I mean.. And I am sure you will find problems in other extensions.
on JEM 2.3.0 stable in latest Joomla (3.9.16) Protostar php7.4.1