ServicePrincipal StartDate and EndDate not displaying Using Graph API In Power Shell

Brahmaiah, I think you're missing a 'foreach' to go through the collection of the expiring SPs (had no chance to look at it more closely). Anyway, please take a look at the script below that generates a decent report for the same purpose.

$tenantID = '<your TenantID>'
$clientID = '<your ClientID>'
$clientSecret = (ConvertTo-SecureString '<your Client Secret>' -AsPlainText -Force)
$accessToken = Get-MsalToken -clientID $clientID -clientSecret $clientSecret -tenantID $tenantID | Select-Object -Property AccessToken

# MS Graph Apps URI
$aadAppsURI = 'https://graph.microsoft.com/v1.0/applications'
# Get Expiring Creds in x Days
$expiryCheck = 60
$now = (Get-Date).ToUniversalTime() 
$expiryLimit = $now.AddDays($expiryCheck)
# MS Graph Directory Audit URI
$signInsURI = 'https://graph.microsoft.com/v1.0/auditLogs/directoryAudits'

# Report Template
$aadAppReportTemplate = [pscustomobject][ordered]@{ 
    displayName     = $null 
    createdDateTime = $null 
    signInAudience  = $null  
} 

# Get Apps
$aadApplications = @()
$aadApps = Invoke-RestMethod -Headers @{Authorization = "Bearer $($accessToken.AccessToken)" } `
    -Uri  $aadAppsURI `
    -Method Get

$aadApps.value.Count

if ($aadApps.value) {
    $aadApplications += $aadApps.value
    # More Apps?
    if ($aadApps.'@odata.nextLink') {
        $nextPageURI = $aadApps.'@odata.nextLink'
        do {
            $aadApps = $null 
            $aadApps = Invoke-RestMethod -Headers @{Authorization = "Bearer $($accessToken.AccessToken)" } `
                -Uri  $nextPageURI `
                -Method Get
            if ($aadApps.value) {
                $aadApplications += $aadApps.value
                $aadApplications.value.Count
            }
            if ($aadApps.'@odata.nextLink') {
                $nextPageURI = $aadApps.'@odata.nextLink'
            }
            else {
                $nextPageURI = $null
            }
        } until (!$nextPageURI)
    }
}

$aadApplications = $aadApplications | Sort-Object -Property createdDateTime -Descending
$aadAppsReport = @()
$expiringCredsApps = @()

foreach ($app in $aadApplications) {
    $blnExpiringCreds = $false 
    # Report Output    
    $reportData = $aadAppReportTemplate.PsObject.Copy()
    $reportData.displayName = $app.displayName
    $reportData.createdDateTime = $app.createdDateTime
    $reportData.signInAudience = $app.signInAudience

    # Key Expiry
    if ($app.keyCredentials) {
        $keys = @()
        foreach ($cred in $app.keyCredentials) {
            [datetime]$keyExpiry = $cred.endDateTime
            if ($keyExpiry -lt $expiryLimit) {
                Write-Warning "$($app.displayName): Key expired/expiring on $($keyExpiry)"
                $blnExpiringCreds = $true
            }
            $keys += $app.keyCredentials | Select-Object -Property @{Name = 'displayName'; Expression = { $cred.displayName } }, @{Name = 'keyId'; Expression = { $cred.keyId } }, @{Name = 'startDateTime'; Expression = { $cred.startDateTime } }, @{Name = 'endDateTime'; Expression = { $cred.endDateTime } }
        }
        $reportData | Add-Member -Type NoteProperty -Name "keyCredentials" -Value @($keys)
    }

    # Password Expiry
    if ($app.passwordCredentials) {
        $passwords = @()
        foreach ($cred in $app.passwordCredentials) {
            [datetime]$keyExpiry = $cred.endDateTime
            if ($keyExpiry -lt $expiryLimit) {
                Write-Warning "$($app.displayName): Password expired/expiring on $($keyExpiry)"
                $blnExpiringCreds = $true
            }
            $passwords += $app.passwordCredentials | Select-Object -Property @{Name = 'displayName'; Expression = { $cred.displayName } }, @{Name = 'keyId'; Expression = { $cred.keyId } }, @{Name = 'startDateTime'; Expression = { $cred.startDateTime } }, @{Name = 'endDateTime'; Expression = { $cred.endDateTime } }
        }
        $reportData | Add-Member -Type NoteProperty -Name "passwordCredentials" -Value @($passwords)
    }

    # SignIns
    $appSignIns = $null 
    $appSignIns = Invoke-RestMethod -Headers @{Authorization = "Bearer $($accessToken.AccessToken)" } `
        -Uri  "$($signInsURI)?&`$filter=targetResources/any(t: t/id eq `'$($app.id)`')" `
        -Method Get
   
    if ($appSignIns.value) {
        "$($app.displayName): $($appSignIns.value.Count) recent signIns"
        $reportData | Add-Member -Type NoteProperty -Name "recentSignIns" -Value $appSignIns.value.Count
    }
    else {
        "$($app.displayName): $($appSignIns.value.Count) recent signIns"
        $reportData | Add-Member -Type NoteProperty -Name "recentSignIns" -Value '0'
    }
    $aadAppsReport += $reportData

    if ($blnExpiringCreds) {
        $expiringCredsApps += $reportData
    }
}

$expiringCredsApps.count 
$expiringCredsApps | Format-Table

# Report 
$aadAppsReport | Format-Table -AutoSize

 Update the information in the first three lines (i.e., TenantID, ClientID, ClientSecret) with the values from your app registration. Make sure that the app you registered has the following permissions (from Microsoft Graph):

• Application.Read.All
• AuditLog.Read.All

Also, The MSAL.PS module is used for Microsoft Graph Authentication. It can be installed with the following command: 

Install-Module -Name MSAL.PS

The first part of the report includes the apps whose credentials will be expiring within the next 60 days (on the number you specified in the ninth line of the script).  The second part includes the recent sign-ins info for the SPs that are already exipired or expiring soon. The third part is all about all the registered apps and the audit log of the recent sign-ins (usability stats).

This is something you can schedule and even expand it further to enable notifications using automation.