correct, the queryable datapage for the data object (in default data sources under settings) is not really that important - its a starting point for Insights to create a virtual report definition on the data object (which will be constructed from the rules in the class, like relevant records, associations, optimized embedded properties etc.).
@Shirisha_Boinapalli 's solution "Scenario 1 - Calendar Days in a Chart" is the right track, in '25 you could specify your own calculations and even custom functions for those calculations to do business days BUT you said you’re on '24.
In '24 the only way to achieve this, for a Chart, would be to physically create this property in your data model and populate it (rather than trying to do it in a response data transform on data page).
Personally, I would look to implement this as an Insight Table or List View, so the users can get to the data, until you can get to '25 and put it in a chart type to enhance the UX.