What is the best way to make a website on wordpress with php code placed on each page?

Question

WordPress

We need a website-personal account with various registration forms, tables, graphs. Almost every page includes php code.

What is the best way to do it in the first place? A couple of options came to mind:

1. Put code in the theme that analyzes the url and loads content depending on the part of the page url

$url_arr = explode( '/', $url );

$page = $url_arr [3]; // https://qna.habr.com/<b>question</b>/new

$action = isset($url_arr [4]) ? $url_arr [4] : '';  // https://qna.habr.com/question/<b>new</b>

switch ($page) {
    case 'reg':
        require $dir . 'reg.php';
        break;
    case 'report':
        require $dir . 'report.php';
        break;
    case 'prefile':
        require $dir . 'prefile.php';
        break;
...
}

2. Create a Plugin with
add_action( 'init', 'pluginname_route' );
and in pluginname_route - put the url parsing function - as shown above

3. Create a Plugin with different functions and insert them as shortcodes on pages.

4. something else