可以组合使用排序和分组....

@'
Name;Employeenumber;Accessrights
Max;123456;ReadOnly
Berta;133556;Write
Jhonny;161771;ReadOnly
Max;123456;Write
'@ |
    ConvertFrom-Csv -Delimiter ';' |
        Sort-Object -Property Name, Accessrights -Descending |
            Group-Object -Property Name |
                ForEach-Object {
                    $_.Group[0]
                }