How to list Exchange Online Dynamic Distribution Group members
The below will allow you to list the members of a dynamic distribution group
Set-ExecutionPolicy RemoteSigned
$UserCredential = Get-Credential
$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://outlook.office365.com/powershell-liveid/ -Credential $UserCredential -Authentication Basic -AllowRedirection
Import-PSSession $Session
$DDG = Get-DynamicDistributionGroup "My DL Name"
Get-Recipient -RecipientPreviewFilter $DDG.RecipientFilter -OrganizationalUnit $DDG.RecipientContainer
Remove-PSSession $Session