Compare two csv files

Skipster311-1 Give this a try. It'll output two files, one containing the devices that are only in the Intune file, and the other with devices that only exist in the Exchange file.

$Intune = Import-CSV .\intune.csv | Group-Object -AsHashTable -AsString -Property 'DeviceID'
$Exchange = Import-CSV .\mobiledevicereport.csv | Group-Object -AsHashTable -AsString -Property 'DeviceID'

$OnlyInIntune = @()
$OnlyInExchange = @()

ForEach ($Device in $Intune.Values) {
    if (!$Exchange[$Device.DeviceID]) {
        $OnlyInIntune += $Device
    }
}

ForEach ($Device in $Exchange.Values) {
    if (!$Intune[$Device.DeviceID]) {
        $OnlyInExchange += $Device
    }
}

$OnlyInIntune | Export-CSV -NoTypeInformation DevicesOnlyInIntune.csv
$OnlyInExchange | Export-CSV -NoTypeInformation DevicesOnlyInExchange.csv