Date: weekends and holidays

You don't need to check those conditions if you have a field as I described. The SUM() measure will automatically respect any filters you apply, so you'll get the count of working days. You can apply a filter with a slicer, a visualization cross-filter, or one of a visual-, page-, or report-level filter.

Your holidays must come from some source table because there are no built in functions that know when your organization has holidays. A weekday check is simple, just check for

// Power Query
WeekdayFlag =
let
  Weekday = Date.DayOfWeek( [Date] )
  ,WeekdayFlag =
    if Weekday > 0 and Weekday < 6
    then 1
    else 0
in
  WeekdayFlag


// DAX
WeekdayFlag =
( WEEKDAY( DimDate[Date] ) > 1
    && WEEKDAY( DimDate[Date] ) < 7
) * 1

Your WorkdayFlag would be as follows:

// Power Query
WorkdayFlag =
if [WeekdayFlag] = 1 and [HolidayFlag] = 0
then 1
else 0



// DAX
WorkdayFlag =
IF(
    DimDate[WeekdayFlag] = 1
        && DimDate[HolidayFlag] = 0
    ,1
    ,0
)

Then your count of working days measure is just:

WorkingDays =
SUM( DimDate[WorkdayFlag] )

Measures automatically respect filter context.