Main site single-property.php design, as homepage of a multisite

You have two options; either bake into the theme (functions.php) or write a simple plugin that auto-creates the post based on hooking into after new site (blog) creation:

https://codex.wordpress.org/Plugin_API/Action_Reference/wpmu_new_blog

Use the insert post function to do the creation:

https://developer.wordpress.org/reference/functions/wp_insert_post/

Then, set as the home page based on ID returned:

update_option( 'page_on_front', $new_page->ID );

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)