Code:
$tx.multiline = 1

Works for me.

 Code:
break on

$sys    = createObject('kixtart.system')
$frm    = $sys.form()

$frm.size = 450, 400
$tx = $frm.textbox
$tx.dock = 5
$tx.multiline = 1
$tx.text = 'ola1'+@crlf+'ola2'+@crlf+'ola3'+@crlf

$frm.show
while $frm.visible
    $=Execute($frm.doevents(1))
    sleep 0.05
    $ln = ubound(Split($tx.text, @crlf))+1
    $lns = ubound(Split(substr($tx.text, 1, $tx.SelectionStart+1), @crlf))+1
    $tx.SelectionStart-1?
    Len($tx.text)-$ln?
    $ln?
    $frm.text =
    "Length:"+Cstr(Len($tx.text))+
    " | Lines:"+cstr($ln)+
    " | Pos:"+Cstr($tx.SelectionStart+1)+
    " | Line pos:"+cstr($lns)
    $lns = 0
    $text = ''
loop