You give the format like this:

<?php
DateTimePicker::create(array(
    "name"=>"myDateTime",
    "format"=>"MM/YYYY"
));
?>

This will trigger the DateTimeFormat to select year and month only. Of course at server-side you will receive the date time in this format "2019-03-01 00:00:00". But you will easy to get the year and month from the format, for example:

$date = DateTime::createFromFormat("Y-m-d H:i:s", "2019-03-01 00:00:00");
$year = $date->format("Y");
$month = $date->format("m");