В конце я добавил "-and $ _ -lt (get-date)"
$FiscalStart = [datetime]'2019-12-31'
$date2 = Get-Date -Hour 0 -Minute 0 -Second 0
1..($date2 - $FiscalStart).Days | % {($FiscalStart).AddDays($_)} |
? { $_.DayOfWeek -eq 'monday' -and $_ -lt (get-date)}
Monday, January 6, 2020 12:00:00 AM
Monday, January 13, 2020 12:00:00 AM
Monday, January 20, 2020 12:00:00 AM
Monday, January 27, 2020 12:00:00 AM
Monday, February 3, 2020 12:00:00 AM