Hi @ネパリ サンデャ,
Unfortunately, there are no settings/options available in SharePoint online lists to show additional fields in right side details pane/unscheduled pane.
Also, this is not possible using SharePoint JSON formatting capabilities as well. SharePoint JSON calendar view formatting only supports adding extra CSS classes to the calendar/event item using additionalEventClass
attribute.
Documentation: SharePoint JSON Calendar view customizations
Personally, I completely agree with you, this is indeed a good addition to the current features of SharePoint. Thank you for bringing things to our attention. We sincerely recommend you go to SharePoint Feedback community to provide your feedback: SharePoint · Community (microsoft.com). This is the best platform to let related team hear from you and make the products and services better for you and others.
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