I still can’t find the source of the problem in the code but here is my changes to make version 2.5 work.
To make the “Themes” page and the “Page Template Box” in the edit “Page” fonctionnal, you have to remove the anchor tag in the Description of the default theme.
(wp-content/default/style.css)
[before]
Description: The default WordPress theme based on the famous Kubrick.
[after]
Description: The default WordPress theme based on the famous Kubrick.
To make the “Plugins” page fonctionnal, you have to remove every anchor tag in the Description of every plugins and also remove the “Plugin URI” and “Author URI” reference.
(wp-content/plugins/hello.php)
[before]
Plugin Name: Hello Dolly
Plugin URI: https://www.ads-software.com/#
Description: This is not just a plugin, it symbolizes the hope and enthusiasm of an entire generation summed up in two words sung most famously by Louis Armstrong: Hello, Dolly. When activated you will randomly see a lyric from <cite>Hello, Dolly</cite> in the upper right of your admin screen on every page.
Author: Matt Mullenweg
Version: 1.5
Author URI: https://photomatt.net/
[after]
Plugin Name: Hello Dolly
Description: This is not just a plugin, it symbolizes the hope and enthusiasm of an entire generation summed up in two words sung most famously by Louis Armstrong: Hello, Dolly. When activated you will randomly see a lyric from <cite>Hello, Dolly</cite> in the upper right of your admin screen on every page.
Author: Matt Mullenweg
Version: 1.5
(wp-content/plugins/askimet/askimet.php)
[before]
Plugin Name: Akismet
Plugin URI: https://akismet.com/
Description: Akismet checks your comments against the Akismet web service to see if they look like spam or not. You need a WordPress.com API key to use it. You can review the spam it catches under "Comments." To show off your Akismet stats just put <?php akismet_counter(); ?> in your template. See also: WP Stats plugin.
Version: 2.1.4
Author: Matt Mullenweg
Author URI: https://photomatt.net/
[after]
Plugin Name: Akismet
Description: Akismet checks your comments against the Akismet web service to see if they look like spam or not. You need a WordPress.com API key to use it. You can review the spam it catches under "Comments." To show off your Akismet stats just put <?php akismet_counter(); ?> in your template. See also: WP Stats plugin.
Version: 2.1.4
Author: Matt Mullenweg