PowerShell script to get user information takes hours to run--any way to do it faster?

This PowerShell script to get a lot of user information from Microsoft 365 and write to csv works fine, but is taking a LONG time to run (like hours) for about 12k users. Is there any way to do this in a faster way? Is there an API I can call from Python that would do this faster?

# Get all users from AAD
$all = get-azureaduser -All $true
# Empty the output file we will use
$path = 'c:\blahblahpath\M365users.csv'
$path -replace ' ', '` '
Clear-Content -Path $path
# Loop through all users, get attributes and write to csv
$all | foreach-object {
$user = $_
$mbx = ""
$fwd = ""
$mbx = get-mailbox $user.userprincipalname -ErrorAction SilentlyContinue
$fwd = $mbx.forwardingsmtpaddress
$extem = $mbx.externalemailaddress
$aliases = $mbx.emailaddresses
# Expanding only the Extension Attributes related to the user and converting the Dictionary to Custom Object
#   so that keys can be accessed through the dot (.) operator
$Extension_Attributes = New-Object Psobject -Property $user.ExtensionProperty 
# Combining the required attributes from the user object and extension_attributes to A single object
$u_properties = [pscustomobject] @{
"UserPrincipalName" = $user.UserPrincipalName
"GivenName" = $user.GivenName
"Surname" = $user.Surname
"M3-DisplayName" = $user.DisplayName
"JobTitle" = $user.JobTitle
"Department" = $user.Department
"CompanyName" = $user.CompanyName
"M3-Mail" = $user.mail
"M3-OtherMails" = $user.OtherMails[0]
"ForwardingSmtpAddress" = $fwd
"ExternalEmailAddress" = $extem
"Aliases" = $aliases
"DeliverToMailboxAndForward" = $keepinmbx
"TelephoneNumber" = $user.TelephoneNumber
"PhysicalDeliveryOfficeName" = $user.PhysicalDeliveryOfficeName
"PreferredLanguage" = $user.PreferredLanguage
"MailNickName" = $user.MailNickName 
"StreetAddress" = $user.StreetAddress
"City" = $user.City
"State" = $user.State
"PostalCode" = $user.PostalCode
"Country" = $user.Country
"UsageLocation" = $user.UsageLocation
"Mobile" = $user.Mobile 
"UserType" = $user.UserType
"AccountEnabled" = $user.AccountEnabled
"LastLogon" = $user.LastLogon
"BlockCredential" = $user.BlockCredential
"AssignedLicenses" = $user.AssignedLicenses
"Created" = $Extension_Attributes.createdDateTime 
"MemberNumber" = $Extension_Attributes.EmployeeID
"TokenExp" = $user.RefreshTokensValidFromDateTime
"OLDMemNumExt" = $Extension_Attributes.extension_60a1274a0a9d4344bd172d81b06d0f50_MemberNumber
"Source" = $Extension_Attributes.extension_06f8dc5952b048a1879af4e793844173_Source
"M3-MemType" = $Extension_Attributes.extension_01816427922e40c9b55cf4364bc171ce_MemType
"M3-Status" = $Extension_Attributes.extension_01816427922e40c9b55cf4364bc171ce_Status
"EmailTeams" = $Extension_Attributes.extension_01816427922e40c9b55cf4364bc171ce_EmailTeams
"M3-EmailCC" = $Extension_Attributes.extension_01816427922e40c9b55cf4364bc171ce_EmailCC
"M3-EmailPri" = $Extension_Attributes.extension_01816427922e40c9b55cf4364bc171ce_EmailPri
"Cert" = $Extension_Attributes.extension_01816427922e40c9b55cf4364bc171ce_Cert
"M3-ExpDate" = $Extension_Attributes.extension_01816427922e40c9b55cf4364bc171ce_ExpDate
"WGTitle" = $Extension_Attributes.extension_01816427922e40c9b55cf4364bc171ce_WGTitle
"ChapTitle" = $Extension_Attributes.extension_01816427922e40c9b55cf4364bc171ce_ChapTitle
"OtherTitle" = $Extension_Attributes.extension_01816427922e40c9b55cf4364bc171ce_LdrTitle
"Othercodes" = $extension_Attributes.extension_11b052b5eb8f4c77973a06876d25a6a4_Othercodes
"ChapCodes" = $extension_Attributes.extension_11b052b5eb8f4c77973a06876d25a6a4_ChapCodes
"WGcodes" = $extension_Attributes.extension_11b052b5eb8f4c77973a06876d25a6a4_WGcodes
"Allcodes" = $extension_Attributes. extension_a14f14664c8e457a856d24680b31c9d4_AllCodes
"Cmems" = $Extension_Attributes.extension_4adef2735ffb4a9dafc9a85188ca512d_Cmems
"M3-isnet" = $Extension_Attributes.extension_01816427922e40c9b55cf4364bc171ce_IsNet
"SipProxyAddress" = $user.SipProxyAddress
}
# check
#write-host "got $u_properties"
$u_properties | Export-csv -Path $path -NoTypeInformation -Force -Append
}#

I timed the $all = get-azureaduser -All $true at about 20 seconds, so obviously the time is in the loop--maybe the 'get-mailbox...' is slow?

I'm fairly novice at PowerShell so I can't think of a lot of other ways to try doing this.

I believe with simply putting Export-Csv as the last statement of your pipeline your script time will improve greatly. Appending to a Csv means that in each loop iteration Export-Csv has to open the FileStream, seek until the EOF, append the new line (a single object) and close the stream. This is a really expensive thing to do 12k times. Instead, if you put it as the last statement, no -Append is needed and the FileStream is kept opened until no more output is coming from your ForEach-Object.

Get-AzureADUser -All $true | ForEach-Object {
    # same logic here
} | Export-Csv -Path $path -NoTypeInformation # here is the last statement, no append needed.

To put it into perspective how bad is -Append inside a loop, you can run the following test:

$test = @{
    'With Append' = {
        $tmp = New-TemporaryFile
        0..12000 | ForEach-Object {
            [pscustomobject]@{
                foo = 'bar'
            } | Export-Csv $tmp.FullName -Append
        }
        $tmp | Remove-Item
    }
    'Pipeline Processing' = {
        $tmp = New-TemporaryFile
        0..12000 | ForEach-Object {
            [pscustomobject]@{
                foo = 'bar'
            }
        } | Export-Csv $tmp.FullName
        $tmp | Remove-Item
    }
}

$test.GetEnumerator() | ForEach-Object {
    [pscustomobject]@{
        Test = $_.Key
        Time = (Measure-Command { & $_.Value }).TotalMilliseconds
    }
}