Date.IsInPreviousMonth

This function checks if the provided datetime value, dateTime, happened in the month before the current date and time on the system. Keep in mind that when a value from the current month is passed to this function, it will return false. The input for this function should be a date, datetime, or datetimezone value.

Check if the month prior to the system's current time falls in the preceding month. Employ the Power Query function MDate.IsInPreviousMonth(Date.AddMonths(DateTime.FixedLocalNow(), -1)) to obtain the result, which will return "true" if the condition is met.