Change the number of plugins counted on wp-admin/plugins.php

The values haven’t any hook to change this. However it is easy to identify the counter via Javascript. You can change this with short lines of Javascript.

Hook

You should hook in this page hook of the plugin page admin_footer-plugins.php, like add_action( 'admin_footer-plugins.php', [ $this, 'change_view_values' ], 11 );

Function include javascript

As example a function below that change counter for the must-use count, but you should only change the selector for the plugin counter. Small hint, the php variable $this->mustuse_total is my store for the new count. You should replace this with your count, a function that get the count of plugins.

/**
 * Change total count for must use values
 *
 * @since   01/09/2014
 * @return  void
 */
public function change_view_values() {

    $current_screen = get_current_screen();
    if ( null === $current_screen || 'plugins-network' !== $current_screen->id ) {
        return;
    }

    $item = sprintf( _n( 'item', 'items', $this->mustuse_total ), number_format_i18n( $this->mustuse_total ) ); ?>

    <script type="text/javascript">
        jQuery( document ).ready( function($) {
            let text,
                value,
                mustuse,
                selector;
            // replace the brackets and set int value
            selector=".mustuse span";
            text = $( selector ).text();
            value = text.replace( '(', '' );
            value = parseInt( value.replace( ')', '' ) );
            // replace and add strings
            mustuse = value + <?php echo $this->mustuse_total; ?>;
            $( selector ).replaceWith( '(' + mustuse + ')' );
            mustuse = mustuse + ' <?php echo esc_attr( $item ); ?>';
            if ( document.URL.search( /plugin_status=mustuse/ ) !== - 1 ) {
                $( '.tablenav .displaying-num' ).replaceWith( mustuse );
            }
        } );
    </script>
    <?php
}

The code is currently in usage in this mu-plugin loader – https://github.com/bueltge/must-use-loader/blob/master/must_use_loader.php#L290

Sreenshot say more

In my context I change the must use counter, easier to understand via the image below.