Ah yes, I forgot that id parameter is actually course module id. So you have two options here:
Alter the link generator to use f parameter instead of id and it would work as is.
protected function newsforumurl() {
$result = false;
if ($forumid = $this->newsforumid()) {
$result = html_writer::link(
new moodle_url('/mod/forum/view.php', ['f' => $forumid]),
"E-mail"
);
}
return $result;
}
Obtain the course module id.
protected function newsforumid() {
global $CFG, $COURSE;
$result = false;
$plugins = \core_plugin_manager::instance()->get_enabled_plugins('mod');
if (isset($plugins['forum'])) {
require_once($CFG->dirroot . '/mod/forum/lib.php');
if ($forum = forum_get_course_forum($COURSE->id, 'news')) {
if ($cm = get_coursemodule_from_id('forum', $forum->id)) {
$result = $cm->id;
}
}
}
return $result;
}