お問合せの回答が無いようなので、当方で改修したコードをペーストします。
対象ファイル：prartsフォルダ内の、common.php をエディターで開き、下記のコードを差替えればメニューを20個まで増やせます。
（ほかのテンプレートのようにサブメニュー化した方が良いかもしれませんので、q19cmsサポート担当様から指示頂いたほうが良いかもしれません）

<?php
// 共通定義
$common_items = array(
"items" => array(
"dummy1" => array(
"title" => "表示関連",
"type" => "comment",
"class" => "openclose",
),
"site_title" => array(
"title" => "サイトタイトル",
"type" => "text",
),
"site_logo" => array(
"title" => "ロゴファイル",
"type" => "image",
),
"site_desc" => array(
"title" => "サイト説明",
"type" => "text",
),
"site_keyword" => array(
"title" => "サイトキーワード",
"type" => "text",
),
"site_image" => array(
"title" => "サイト画像",
"type" => "image",
"info" => "SNSなどで参照された際に表示されます",
),
"dummy2-1" => array(
"title" => "メニュー１",
"type" => "comment",
"class" => "openclose",
),
"menu1_title" => array(
"title" => "メニュー1",
"type" => "text",
),
"menu1_link" => array(
"title" => "リンク1",
"type" => "text",
),
"dummy2-2" => array(
"title" => "メニュー２",
"type" => "comment",
"class" => "openclose",
),
"menu2_title" => array(
"title" => "メニュー2",
"type" => "text",
),
"menu2_link" => array(
"title" => "リンク2",
"type" => "text",
),
"dummy2-3" => array(
"title" => "メニュー３",
"type" => "comment",
"class" => "openclose",
),
"menu3_title" => array(
"title" => "メニュー3",
"type" => "text",
),
"menu3_link" => array(
"title" => "リンク3",
"type" => "text",
),
"dummy2-4" => array(
"title" => "メニュー４",
"type" => "comment",
"class" => "openclose",
),
"menu4_title" => array(
"title" => "メニュー4",
"type" => "text",
),
"menu4_link" => array(
"title" => "リンク4",
"type" => "text",
),
"dummy2-5" => array(
"title" => "メニュー５",
"type" => "comment",
"class" => "openclose",
),
"menu5_title" => array(
"title" => "メニュー5",
"type" => "text",
),
"menu5_link" => array(
"title" => "リンク5",
"type" => "text",
),
"dummy2-6" => array(
"title" => "メニュー６",
"type" => "comment",
"class" => "openclose",
),
"menu6_title" => array(
"title" => "メニュー6",
"type" => "text",
),
"menu6_link" => array(
"title" => "リンク6",
"type" => "text",
),
"dummy2-7" => array(
"title" => "メニュー７",
"type" => "comment",
"class" => "openclose",
),
"menu7_title" => array(
"title" => "メニュー7",
"type" => "text",
),
"menu7_link" => array(
"title" => "リンク7",
"type" => "text",
),
"dummy2-8" => array(
"title" => "メニュー８",
"type" => "comment",
"class" => "openclose",
),
"menu8_title" => array(
"title" => "メニュー8",
"type" => "text",
),
"menu8_link" => array(
"title" => "リンク8",
"type" => "text",
),
"dummy2-9" => array(
"title" => "メニュー９",
"type" => "comment",
"class" => "openclose",
),
"menu9_title" => array(
"title" => "メニュー9",
"type" => "text",
),
"menu9_link" => array(
"title" => "リンク9",
"type" => "text",
),
"dummy2-10" => array(
"title" => "メニュー10",
"type" => "comment",
"class" => "openclose",
),
"menu10_title" => array(
"title" => "メニュー10",
"type" => "text",
),
"menu10_link" => array(
"title" => "リンク10",
"type" => "text",
),
"dummy2-11" => array(
"title" => "メニュー11",
"type" => "comment",
"class" => "openclose",
),
"menu11_title" => array(
"title" => "メニュー11",
"type" => "text",
),
"menu11_link" => array(
"title" => "リンク11",
"type" => "text",
),
"dummy2-12" => array(
"title" => "メニュー12",
"type" => "comment",
"class" => "openclose",
),
"menu12_title" => array(
"title" => "メニュー12",
"type" => "text",
),
"menu12_link" => array(
"title" => "リンク12",
"type" => "text",
),
"dummy2-13" => array(
"title" => "メニュー13",
"type" => "comment",
"class" => "openclose",
),
"menu13_title" => array(
"title" => "メニュー13",
"type" => "text",
),
"menu13_link" => array(
"title" => "リンク13",
"type" => "text",
),
"dummy2-14" => array(
"title" => "メニュー14",
"type" => "comment",
"class" => "openclose",
),
"menu14_title" => array(
"title" => "メニュー14",
"type" => "text",
),
"menu14_link" => array(
"title" => "リンク14",
"type" => "text",
),
"dummy2-15" => array(
"title" => "メニュー15",
"type" => "comment",
"class" => "openclose",
),
"menu15_title" => array(
"title" => "メニュー15",
"type" => "text",
),
"menu15_link" => array(
"title" => "リンク15",
"type" => "text",
),
"dummy2-16" => array(
"title" => "メニュー16",
"type" => "comment",
"class" => "openclose",
),
"menu16_title" => array(
"title" => "メニュー16",
"type" => "text",
),
"menu16_link" => array(
"title" => "リンク16",
"type" => "text",
),
"dummy2-17" => array(
"title" => "メニュー17",
"type" => "comment",
"class" => "openclose",
),
"menu17_title" => array(
"title" => "メニュー17",
"type" => "text",
),
"menu17_link" => array(
"title" => "リンク17",
"type" => "text",
),
"dummy2-18" => array(
"title" => "メニュー18",
"type" => "comment",
"class" => "openclose",
),
"menu18_title" => array(
"title" => "メニュー18",
"type" => "text",
),
"menu18_link" => array(
"title" => "リンク18",
"type" => "text",
),
"dummy2-19" => array(
"title" => "メニュー19",
"type" => "comment",
"class" => "openclose",
),
"menu19_title" => array(
"title" => "メニュー19",
"type" => "text",
),
"menu19_link" => array(
"title" => "リンク19",
"type" => "text",
),
"dummy2-20" => array(
"title" => "メニュー20",
"type" => "comment",
"class" => "openclose",
),
"menu20_title" => array(
"title" => "メニュー20",
"type" => "text",
),
"menu20_link" => array(
"title" => "リンク20",
"type" => "text",
),
"dummy2-21" => array(
"title" => "メニュー下",
"type" => "comment",
"class" => "openclose",
),
"banner" => array(
"title" => "バナー画像",
"type" => "image",
),
"banner_link" => array(
"title" => "バナーリンク",
"type" => "text",
),
"dummy4" => array(
"title" => "共通",
"type" => "comment",
"class" => "openclose",
),
"footer_title" => array(
"title" => "フッタータイトル",
"type" => "text",
),
"footer_text" => array(
"title" => "フッターテキスト",
"type" => "textarea",
),
"map_title" => array(
"title" => "地図タイトル",
"type" => "text",
),
"map_text" => array(
"title" => "地図説明",
"type" => "textarea",
),
"map_url" => array(
"title" => "地図URL",
"type" => "text",
"info" => "GoogleMapの埋め込み（iframe）のURL",
),
"copyright" => array(
"title" => "著作権表示",
"type" => "text",
),
"head_tag" => array(
"title" => "</head>前挿入",
"type" => "textarea",
"info" => "Google Analyticsのタグなどの挿入",
),
"body_tag" => array(
"title" => "</body>前挿入",
"type" => "textarea",
"info" => "Google Analyticsのタグなどの挿入",
),
"dummy5" => array(
"title" => "SNS",
"type" => "comment",
"class" => "openclose",
),
"sns1" => array(
"title" => "X(旧Twitter)",
"type" => "text",
),
"sns2" => array(
"title" => "LINE",
"type" => "text",
),
"sns3" => array(
"title" => "YouTube",
"type" => "text",
),
"sns4" => array(
"title" => "INSTAGRAM",
"type" => "text",
),
"sns5" => array(
"title" => "FaceBook",
"type" => "text",
),
"sns6" => array(
"title" => "その他",
"type" => "text",
),
"dummy7" => array(
"title" => "認証",
"type" => "comment",
"class" => "openclose",
),
"login_id" => array(
"title" => "ログインID",
"type" => "text",
"info" => "ログインIDが不要の場合は、空欄にしてください。",
),
"passwd" => array(
"title" => "パスワード",
"type" => "text",
),
),
"func" => "func_common",
);

// 共通データの変換
function func_common($def, $info)
{
// メニュー
$menu = array();
for ($i = 1; $i <= 20; $i++) {
$title = $info["menu" . $i . "_title"];
$link = $info["menu" . $i . "_link"];
if ($title && $link) {
unset($item);
$item["title"] = $title;
$item["link"] = $link;
// サブメニュー
$sub = array();
for ($j = 1; $j <= 20; $j++) {
$subtitle = $info["menu" . $i . "_sub" . $j . "_title"];
$sublink = $info["menu" . $i . "_sub" . $j . "_link"];
if ($subtitle && $sublink) {
$subitem["title"] = $subtitle;
$subitem["link"] = $sublink;
$sub[] = $subitem;
}
}
if ($sub) {
$item["submenu"] = $sub;
}
$menu[] = $item;
}
}
$info["menu"] = $menu;
// フッターメニュー
$footer_menu = array();
for ($i = 1; $i <= 20; $i++) {
$group = array();
$group_title = $info["footer_menu" . $i . "_title"];
if ($group_title) {
$group["title"] = $group_title;
$menu = array();
for ($j = 1; $j <= 20; $j++) {
$title = $info["footer_menu" . $i . "_item" . $j . "_title"];
$link = $info["footer_menu" . $i . "_item" . $j . "_link"];
if ($title && $link) {
$item["title"] = $title;
$item["link"] = $link;
$menu[] = $item;
}
}
if ($menu) {
$group["menu"] = $menu;
$footer_menu[] = $group;
}
}
}
$info["footer"] = $footer_menu;
// ロゴ
if ($info["site_logo"]) {
$f = Image::getData(intval($info["site_logo"]));
if ($f) {
$info["site_logo_file"] = "user_data/" . $f["save_name"];
}
}
if ($info["site_logo2"]) {
$f = Image::getData(intval($info["site_logo2"]));
if ($f) {
$info["site_logo2"] = "user_data/" . $f["save_name"];
}
}
//
if ($info["banner"]) {
$f = Image::getData(intval($info["banner"]));
if ($f) {
$info["banner_file"] = $f["save_name"];
}
}
//
$login = get_setup();
$info["license"] = $login["license"];
//
return $info;
}