The code below will list the Global Admins in your Azure AD. Note that if using privileged identity management any users currently elevated would also show.
$role = Get-AzureADDirectoryRole | Where-Object {$_.displayName -eq 'Company Administrator'} Get-AzureADDirectoryRoleMember -ObjectId $role.ObjectId
Also note the PowerShell/Graph API name for Global Admins is Company Administrator.