Need help on power query

Here is a methodology you may be able to apply to your case.

A brief explanation.

Set a list of holiday names. 

Set the working start and end times.

Determine the day of the week of the created datetime. (Using Day.Monday makes Monday day 0)

Compare the created time of the created datetime to the working end time. If the created time is after the working end time then advance the created date by one day.

Now look at the day of the week of the amended created date. If it is Saturday or Sunday then advance the created day to the next Monday. (Call this the effective start date.)

Create a list of dates from the effective start date to and including the close date.

Remove any days from the holiday list from the created date list and then remove any remaining days that are Saturdays or Sundays from the list.

Count the number of rows left in the list and that should be the number of working days.
Hope this gets you pointed in the right direction.

let
    HolidayList = {
        #date(2025, 3, 30), #date(2025, 3, 31), #date(2025, 4, 1), #date(2025, 4, 2),
        #date(2025, 6, 5), #date(2025, 6, 8), #date(2025, 6, 9), #date(2025, 6, 10)
    },
    WorkingStart = #time(8, 0, 0),
    WorkingEnd = #time(17, 0, 0),
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("LcpLCsAwCAXAqxTXAT8vaRKvIt7/Gq3gdpgIErAuNrH1yHUsGjS5QV/HphxBYGiblVXaDeKwTmpt12elX06LOg5lfg==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Created_DateTime = _t, Close_DateTime = _t]),
    set_types = 
    Table.TransformColumnTypes(
        Source,
        {{"Created_DateTime", type datetime}, {"Close_DateTime", type datetime}}
    ),
    workingDayCount = 
    Table.AddColumn(
        set_types, 
        "WorkingDuration", 
        each 
        let
            dayOfWeek =             //Assuming workdays are Monday to Friday, this sets Monday as day 0
            Date.DayOfWeek(
                [Created_DateTime], 
                Day.Monday
            ),
            workEndDate =           //if the created time is after working hours the created date is advanced to the next day.
            if Time.From([Created_DateTime]) > WorkingEnd 
                then Date.From(Date.AddDays([Created_DateTime], 1)) 
                else Date.From([Created_DateTime]
            ),
            effectiveStartDate =    //if the workEndDate is after Friday (day 4 in a zero index list) the date is advanced by the number of days required to get to the next Monday.
            if dayOfWeek > 4 
                then Date.AddDays(workEndDate, (7-dayOfWeek)) 
                else workEndDate,
            initialList =           //create a list of dates from the effective start date to and including the clost date.
            List.Dates(
                effectiveStartDate, 
                Number.Round(Number.From(Date.From([Close_DateTime]) - effectiveStartDate), 0) + 1, 
                #duration(1,0,0,0)
            ),
            dayDuration =           //remove the holiday dates and Saturdays and Sundays from the created list and then count the number rows in the list
            List.Count(
                List.Select(
                    List.Difference(initialList, HolidayList), 
                    each Date.DayOfWeek(_, Day.Monday) <> 5 and Date.DayOfWeek(_, Day.Monday) <> 6
                )
            )
        in
            dayDuration,
        type number
    )
in
    workingDayCount