[YankForum]

so for your reference here is the solution:

{vb:data canUsePmSystem, content_privatemessage, canUsePmSystem}
{vb:data folders, content_privatemessage, fetchSummary}
{vb:set folderlist, {vb:raw folders.folders}}
<vb:if condition="$canUsePmSystem">
{vb:set folder, {vb:raw folderlist.messages} }
{vb:set routeInfo.folderid, {vb:raw folder.folderid}}
<vb:if condition="!empty($folder['qty'])">
IF YOU HAVE NEW PRIVATE MESSAGES THIS SHOWS UP
</vb:if>

i dont know if it's the best answer or not but it works! found this in vb message_navigation_menu (vb default theme)
seems you have to define variables first and then assign them values and then use them in if conditions
too many lines of codes for a simple check!