Running 7-Zip from within a Powershell script

Found this script and adapted it to your needs. Can you please try:

$7zipPath = "$env:ProgramFiles\7-Zip\7z.exe"

if (-not (Test-Path -Path $7zipPath -PathType Leaf)) {
    throw "7 zip file '$7zipPath' not found"
}

Set-Alias Start-SevenZip $7zipPath

$Source = "c:\BackupFrom\backMeUp.txt"
$Target = "c:\BackupFolder\backup.zip"

Start-SevenZip a -mx=9 $Target $Source