This was originally needed to change the date stamp on the parent folder of some files so that the date modified matched that of the child files after a OneDrive sync to a new computer caused the parent folder to show the date of the sync, no it's original modified date.

Then this nice person did all the work and published it in a post here: https://superuser.com/questions/926053/change-the-modified-date-of-a-folders-in-possibly-powershell

I'm keeping it here for further development in order to help organize semi-large photos folders…

Get-ChildItem $root |
    Where-Object { $_.PSIsContainer } |
Foreach-Object{
 
    $oldest = Get-ChildItem $_.FullName |
        Where-Object { ! $_.PSIsContainer } |
            Sort-Object LastWriteTime |
    Select-Object -Last 1
 
    if($oldest)
    {
        $_ | Set-ItemProperty -Name CreationTime -Value $oldest.LastWriteTime 
        $_ | Set-ItemProperty -Name LastWriteTime -Value $oldest.LastWriteTime
    }
    else
    {
        # current directory is empty, directory LastWriteTime is left unchanged
        Write-Warning "Directory '$($_.FullName)' is empty, skiping..."
    }
}

And the Created/Modified/Accessed Win GUI equivalents in Powershell are: CreationTime = Created
LastWriteTime = Modified
LastAccessTime = Accessed