I'm trying to get all iOS devices from Intune with Graph.
Whent testing in Graph Explorer with

"https://graph.microsoft.com/v1.0/deviceManagement/managedDevices?$filter=startswith(operatingSystem, 'iOS')&$select=UserPrincipalName,deviceName,managedDeviceOwnerType,managementState,operatingSystem,complianceState,osVersion,model,manufacturer,imei,serialNumber,phoneNumber,userDisplayName,managementCertificateExpirationDate,emailAddress,id"

I get the right result (one iOS device). But when my script it also shows the Windows devices

# A script to fetch iOS device data from the Microsoft Graph and export it to xlsx file.  
#  
CLS  

$AppId = -
$TenantId = -  
$AppSecret = -  
  
# Construct URI and body needed for authentication  
$uri = "https://login.microsoftonline.com/$tenantId/oauth2/v2.0/token"  
$body = @{  
    client_id     = $AppId  
    scope         = "https://graph.microsoft.com/.default"  
    client_secret = $AppSecret  
    grant_type    = "client_credentials" }  
  
# Get OAuth 2.0 Token  
$tokenRequest = Invoke-WebRequest -Method Post -Uri $uri -ContentType "application/x-www-form-urlencoded" -Body $body -UseBasicParsing  
  
# Unpack Access Token  
$token = ($tokenRequest.Content | ConvertFrom-Json).access_token  
  
# Base URL  
$headers = @{Authorization = "Bearer $token"}  
  
# Get Device data  
Write-Host "Accessing the Graph to get user sign-in data..."  
$URI = "https://graph.microsoft.com/v1.0/deviceManagement/managedDevices?$filter=startswith(operatingSystem, 'iOS')&$select=UserPrincipalName,deviceName,managedDeviceOwnerType,managementState,operatingSystem,complianceState,osVersion,model,manufacturer,imei,serialNumber,phoneNumber,userDisplayName,managementCertificateExpirationDate,emailAddress,id"  
$SignInData = (Invoke-RestMethod -Uri $URI -Headers $Headers -Method Get -ContentType "application/json")   

$Report = [System.Collections.Generic.List[Object]]::new()   
  
Foreach ($Device in $SignInData.Value) {    
       
   $ReportLine  = [PSCustomObject] @{            
     UPN                = $Device.UserPrincipalName  
     DeviceName         = $Device.deviceName 
     mdType             = $Device.managedDeviceOwnerType
     ManagementState    = $Device.managementState
     OperatingSystem    = $Device.operatingSystem
     ComplianceState    = $Device.complianceState
     osVersion          = $Device.osVersion
     Model              = $Device.model
     Manufacturer       = $Device.manufacturer
     IMEI               = $Device.imei
     SerialNumber       = $Device.serialNumber
     PhoneNumber        = $Device.phoneNumber
     UserDisplayName    = $Device.userDisplayName
     MDMCertificateExp  = $Device.managementCertificateExpirationDate
     Email              = $Device.emailAddress  
     Id                 = $Device.Id }
     $Report.Add($ReportLine)   
} # End ForEach  

  
Write-Host "All done. " $Report.Count "accounts processed - output available in c:\Temp\ReportiOSDevices.xlsx."  
  
$Report | Export-Excel c:\Temp\ReportiOSDevices.xlsx