Default Group Privacy Setting

A more advance version based on classification:

#...................................
# Variables:
#   Cut off date in days
#   Classification
#...................................
$cutoffdate = ((Get-Date).AddDays(-10))
$classification = "High"

# Retrieve recently created groups with accesstype set to PUBLIC
$Groups = Get-UnifiedGroup | Where-Object {
    $_.WhenCreated -ge $cutoffdate -and $_.AccessType -eq 'Public' -and $_.Classification -eq $classification } `
     | Sort-Object whencreated | Select DisplayName, WhenCreated, AccessType, Classification, ManagedBy

# For each new group update set accesstype to PRIVATE
ForEach ($G in $Groups) {
    Set-UnifiedGroup -Identity $G.DisplayName -AccessType 'Private'
    Write-Host "The following Group privacy setting was updated:" $G.DisplayName
}