If you modified a plugin and don’t want it to appear in the updates list, use this function from rniswonger in your functions.php

/**
 * Prevent update notification for plugin
 * http://www.thecreativedev.com/disable-updates-for-specific-plugin-in-wordpress/
 * Place in theme functions.php or at bottom of wp-config.php
 */
 function disable_plugin_updates( $value ) {
    $pluginsToDisable = [
        'plugin-folder/plugin.php',
        'plugin-folder2/plugin2.php'
    ];
    if ( isset($value) && is_object($value) ) {
        foreach ($pluginsToDisable as $plugin) {
            if ( isset( $value->response[$plugin] ) ) {
                unset( $value->response[$plugin] );
            }
        }
    }
    return $value;
}
add_filter( 'site_transient_update_plugins', 'disable_plugin_updates' );