Date.IsInPreviousWeek Start Week with Monday

Unfortunately, as ImkeF points out, there isn't a parameter to modify this function to work like you want it to.

However, you can write your own equivalent function using functions that do have such a parameter, like Date.StartOfWeek.

This should give you the start of the current week:

Date.StartOfWeek(Date.From(DateTime.LocalNow()), Day.Monday)

Then you can write a custom column like

[Date] >= Date.AddWeeks([WeekStart], -1) and [Date] < [WeekStart]

Here's a full query version that defines WeekStart as a constant rather than materializing it as an custom column:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjTQt9Q3MjAyUorVAfOACIVriMo1QuUao3JNULmmqFwzVK45KtcCyo0FAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Date = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Date", type date}}),
    #"Added Weekday" = Table.AddColumn(#"Changed Type", "Weekday", each Date.DayOfWeekName([Date]), type text),
    WeekStart = Date.StartOfWeek(Date.From(DateTime.LocalNow()), Day.Monday),
    #"Added IsInPrevWeek" = Table.AddColumn(#"Added Weekday", "IsInPrevWeek", each [Date] >= Date.AddWeeks(WeekStart, -1) and [Date] < WeekStart, type logical)
in
    #"Added IsInPrevWeek"