Creating azure AD app using az powershell

I am creating an azure AD app, generating a client secret for it, and giving Reader role using az PowerShell
I want to give Microsoft Graph. Directory.readAll permission to the app, but not sure how to do using PowerShell. Can anyone help?
Here is the code I've written:

#Connect to Azure AD
Connect-AzAccount -TenantId <tenant-id>
Connect-AzureAD
#Set variables for the app
$appName = "test"
$secret = "MySecret"

#Create the app
$app = New-AzureADApplication -DisplayName $appName -PublicClient $false

#Create the client secret
$bytes = [System.Text.Encoding]::Unicode.GetBytes($secret)
$base64 = [System.Convert]::ToBase64String($bytes)
$startDate = Get-Date
$endDate = $startDate.AddYears(1)
$secret = New-AzureADApplicationPasswordCredential -ObjectId $app.ObjectId -CustomKeyIdentifier "MyCustomKeyIdentifier" -Value $base64 -StartDate $startDate -EndDate $endDate

#Retrieve the tenant ID
$tenantId = (Get-AzureADTenantDetail).ObjectId

#giving Reader Role
New-AzRoleAssignment -ObjectId $app.ObjectId -RoleDefinitionName "Reader" -PrincipalType "ServicePrincipal"

#Print the App-ID, tenant ID, and client secret
Write-Host "App-ID: $($app.AppId)"
Write-Host "Tenant ID: $tenantId"
Write-Host "Client Secret: $($secret.Value)"

I tried to reproduce the same in my environment and got below results:

I ran same PowerShell script as you and got response like below:

#Connect to Azure AD
Connect-AzAccount -TenantId <tenantID>
Connect-AzureAD

#Set variables for the app
$appName = "test"
$secret = "MySecret"

#Create the app
$app = New-AzureADApplication -DisplayName $appName -PublicClient $false

#Create the client secret
$bytes = [System.Text.Encoding]::Unicode.GetBytes($secret)
$base64 = [System.Convert]::ToBase64String($bytes)
$startDate = Get-Date
$endDate = $startDate.AddYears(1)
$secret = New-AzureADApplicationPasswordCredential -ObjectId $app.ObjectId -CustomKeyIdentifier "MyCustomKeyIdentifier" -Value $base64 -StartDate $startDate -EndDate $endDate

#Retrieve the tenant ID
$tenantId = (Get-AzureADTenantDetail).ObjectId

#giving Reader Role
New-AzRoleAssignment -ObjectId $app.ObjectId -RoleDefinitionName "Reader" -PrincipalType "ServicePrincipal" -Scope "/subscriptions/<subID>/resourcegroups/<myRGname>"

#Print the App-ID, tenant ID, and client secret
Write-Host "App-ID: $($app.AppId)"
Write-Host "Tenant ID: $tenantId"
Write-Host "Client Secret: $($secret.Value)"

Response:

When I checked the same in Portal, application named test created successfully like below:

To add Microsoft Graph Directory.Read.All permission to this application, you can run below PowerShell script:

$Graph = New-Object -TypeName "Microsoft.Open.AzureAD.Model.RequiredResourceAccess"
$Graph.ResourceAppId = "00000003-0000-0000-c000-000000000000"
$DirectoryReadAll = New-Object -TypeName "Microsoft.Open.AzureAD.Model.ResourceAccess" -ArgumentList "7ab1d382-f21e-4acd-a863-ba3e13f7da61","Role"
$Graph.ResourceAccess = $DirectoryReadAll
$app = Get-AzureADApplication -SearchString "test" 
  
Set-AzureADApplication -ObjectId $app.ObjectId -RequiredResourceAccess $Graph

Response:

When I checked the same in Portal, Directory.Read.All permission added to the application successfully like below:

To grant admin consent to above permission, you need to create service principal and run PowerShell script like below:

$sp = New-AzureADServicePrincipal -AccountEnabled $true -AppId $app.AppId -AppRoleAssignmentRequired $true -DisplayName "test"
$graphsp = Get-AzureADServicePrincipal -Filter "AppId eq '00000003-0000-0000-c000-000000000000'"

New-AzureADServiceAppRoleAssignment `
             -Id $DirectoryReadAll.Id `
             -ObjectId $sp.ObjectId `
             -PrincipalId $sp.ObjectId `
             -ResourceId $graphsp.ObjectId

Response:

To confirm that, you can check Portal where admin consent is granted successfully like below: