Add plugin to set default HTTPS siteurl for new blogs

https-siteurl.php

+<?php
+/*
+ * Plugin Name: A/I - Default HTTPS siteurl
+ * Description: Set the default siteurl to HTTPS for new blogs
+ * Version: 0.0.1
+ * Author: Autistici/Inventati
+ * Author URI: https://autistici.org
+ */
+
+add_filter('wp_initialize_site_args', function($args, $site) {
+    $url = untrailingslashit('https://' . $site->domain . $site->path);
+
+    $args['options']['home'] = $url;
+    $args['options']['siteurl'] = $url;
+
+    return $args;
+}, 10, 2);