Get the TeamsMessagesDataFolder

gistfile1.txt

$folderid= new-object Microsoft.Exchange.WebServices.Data.FolderId([Microsoft.Exchange.WebServices.Data.WellKnownFolderName]::Inbox,$MailboxName)   
$TeamsMessagesDataFolderEntryId = new-object Microsoft.Exchange.WebServices.Data.ExtendedPropertyDefinition([System.Guid]::Parse("{E49D64DA-9F3B-41AC-9684-C6E01F30CDFA}"), "TeamsMessagesDataFolderEntryId", [Microsoft.Exchange.WebServices.Data.MapiPropertyType]::Binary);
$psPropset= new-object Microsoft.Exchange.WebServices.Data.PropertySet([Microsoft.Exchange.WebServices.Data.BasePropertySet]::FirstClassProperties) 
$psPropset.Add($TeamsMessagesDataFolderEntryId)
$RootFolder = [Microsoft.Exchange.WebServices.Data.Folder]::Bind($service,$folderid,$psPropset)        
if ($RootFolder.TryGetProperty($TeamsMessagesDataFolderEntryId,[ref]$FolderIdVal))
{
     $TeamsMessagesFolderId= new-object Microsoft.Exchange.WebServices.Data.FolderId((ConvertId -HexId ([System.BitConverter]::ToString($FolderIdVal).Replace("-","")) -service $service))
     $TeamsMessagesDataFolder = [Microsoft.Exchange.WebServices.Data.Folder]::Bind($service,$TeamsMessagesFolderId);
}       
        
function ConvertId{    
    param (
            [Parameter(Position=1, Mandatory=$false)] [String]$HexId,
            [Parameter(Position=2, Mandatory=$false)] [Microsoft.Exchange.WebServices.Data.ExchangeService]$service
       )
    process{
        $aiItem = New-Object Microsoft.Exchange.WebServices.Data.AlternateId      
        $aiItem.Mailbox = $MailboxName      
        $aiItem.UniqueId = $HexId   
        $aiItem.Format = [Microsoft.Exchange.WebServices.Data.IdFormat]::HexEntryId      
        $convertedId = $service.ConvertId($aiItem, [Microsoft.Exchange.WebServices.Data.IdFormat]::EwsId) 
     return $convertedId.UniqueId
    }
   }

You need to logon as a normal user that has been delegate access to the Group mailbox then right client and root folder choose the middle option and enter in the Email address from the Group mailbox

Thank you, it helped me a bit, but still not helping to get the actual functionality. With the above I am able to see the content of the folder "Top of Information Store". that doesn't have any TeamMessagesdata folder.
Unable to connect to the root folder.
The below error is coming, the logged on user has the delegate access to the group mailbox and also has compliance administrator and global administrator assigned.
suggest me if anything is missing w.r.t roles or permission.

BTW , the below is the error, when I am trying to expand the root tress structure

Did you try to add Full Permissions via add-mailboxpermission ? the other thing would be try to retrieve it via code instead it could just be a bug in that app