Disabled users who still have licences

#Requires -Modules Microsoft.Graph.Authentication, Microsoft.Graph.Users, Microsoft.Graph.Identity.DirectoryManagement
# Disabled user accounts that still have licences assigned. Read-only.

Connect-MgGraph -Scopes 'User.Read.All', 'LicenseAssignment.Read.All' -NoWelcome

$skuNames = @{}
Get-MgSubscribedSku -All | ForEach-Object { $skuNames[$_.SkuId] = $_.SkuPartNumber }

Get-MgUser -All -Filter 'accountEnabled eq false' -Property 'id', 'displayName', 'userPrincipalName', 'assignedLicenses', 'licenseAssignmentStates', 'onPremisesSyncEnabled' |
    Where-Object { $_.AssignedLicenses.Count -gt 0 } |
    ForEach-Object {
        $licences = $_.AssignedLicenses | ForEach-Object {
            if ($skuNames.ContainsKey($_.SkuId)) { $skuNames[$_.SkuId] } else { $_.SkuId }
        }
        [pscustomobject]@{
            UserPrincipalName = $_.UserPrincipalName
            DisplayName       = $_.DisplayName
            Licences          = $licences -join ', '
            ViaGroup          = @($_.LicenseAssignmentStates | Where-Object { $_.AssignedByGroup }).Count -gt 0
            SyncedFromAD      = $_.OnPremisesSyncEnabled -eq $true
        }
    } |
    Sort-Object UserPrincipalName

Checked automatically against Microsoft's published cmdlet reference. KBY hasn't run it in your tenant; run it in a test environment first.

Reading the output

• assignedLicenses includes licences inherited from groups. ViaGroup is True when at least one licence comes from group-based licensing; those have to be removed by taking the user out of the group (or changing the group's licences), not from the user.
• Licences are shown by SKU part number (for example SPE_E3). Microsoft's product names and service plan identifiers page maps part numbers to product names.
• Accounts synced from on-premises Active Directory are marked SyncedFromAD; disabling or deleting them happens in AD.

Sources

The Microsoft reference page for every cmdlet the script calls, plus the API and product pages behind each permission and caveat.