Change website directory safely to add a static page on startup

Unless I am completely misunderstanding what you are trying to do, there is no need to move your site into a sub-folder.

The easiest way to do what you want is to simply create your static page in normal html just as you want it to appear. Then add the following code to the very top of your page…

<?php /* Template Name: Front Page */ ?>

Then save it as front-page.php and put it in your current theme directory.

Refresh WordPress and voila! you should see your static page.

Alternatively or if that does not work you can name it something else like my-static-front-page.php, then create a new page in WordPress, call it whatever you want, leave the content blank, and just choose the “Front Page” template you created, and publish that page. Then in the dashboard go to Settings > Reading and choose Front Page Displays... a static page. From the front page dropdown choose the page you just created.