Identify files that are not backed up and move them to a new sub folder. Already backed up filenames are in filelist.txt

MoveMissingFilesToFolder.ps1

$dir = 'D:\sample_folder'
$FileList = $dir + '\filelist.txt'
$BackupFolderName = (get-item $dir).BaseName + " Backup"
$BackupFolder = Join-Path $dir $BackupFolderName
New-Item -ItemType Directory -Force -Path $BackupFolder
$BackedFiles = Get-Content $FileList
$Files = Get-ChildItem -Path $dir -File

foreach ($file in $Files) 
{ 
    if($BackedFiles -notcontains $file.Name) 
        {Move-Item $dir\$file $BackupFolder}
}