Database Manager – WP Adminer

• In the case of single site WordPress installations, only Administrators have access in WP Adminer, because by default only administrator have the manage_options capability.
• In the case of WordPress Multisite installations, only Super Admins have access in WP Adminer, because by default only Super Admins have the manage_network_options capability.
• In all cases, the manage_wp_adminer capability now (versions 4.3.0 and above) grants access to WP Adminer. You can assign this capability to a role via code or through the User Role Editor plugin.

Just use the filter pexlechris_adminer_access_capabilities and return the array of desired capabilities that you want to have access to WP Adminer.
For roles, just use the corresponding capabilities, while checking against particular roles in place of a capability is supported in part, this practice is discouraged as it may produce unreliable results.

This issue maybe is due to the caching engine that your browser OR server uses!
* You can try to whitelist the WP Adminer URL, OR
* You can change the WP Adminer URL to a URL that is already whitelisted. For example:
define( ‘PEXLECHRIS_ADMINER_SLUG’, ‘wp-admin/adminer’);

You need to use action pexlechris_adminer_head as follows:

  add_action('pexlechris_adminer_head', function(){      // Use the appropriate get_nonce() function based on your WP Adminer version      $nonce = function_exists('Adminer\get_nonce')          ? Adminer\get_nonce() // For WP Adminer v4.0.0 and newer          : get_nonce(); // For WP Adminer versions below 4.0.0      ?>      <script nonce="<?php echo esc_attr( $nonce )?>"> // get_nonce is an adminer function         // Place your JS code here      </script>      <style>         /* Place your CSS code here */      </style>      <?php   }); 

You can do this using WP filter: pexlechris_adminer_adminbar_dropdown_items.
Filter’s PHPDoc:

 /**   * The dropdown items.   *   * @param array $dropdown_items{   *      @type string $name. The table name.   *      @type string $label. The label of the dropdown item.   *      @type array $args. The array of extra url parameters. Parameters will not be encoded.   *                         Developers could avoid defining args in the array   * }   */  $dropdown_items = apply_filters('pexlechris_adminer_adminbar_dropdown_items', $dropdown_items); 

In Adminer’s website there is documentation about Adminer plugins and Adminer extensions.
In order to define function adminer_object() before this plugin define it, you need to define it inside the hook pexlechris_adminer_before_adminer_loads.
More in the phpDoc below:

 /**   * adminer_object can be overridden, in WP action pexlechris_adminer_before_adminer_loads.   * If a developer want to make his/her own changes (adding plugins, extensions or customizations),   * it is strongly recommended to include_once the class Pexlechris_Adminer and extend it and   * make adminer_object function return his/her new class.   *   * It is strongly recommended, because Pexlechris_Adminer class contains WordPress/Adminer integration (auto login with WordPress credentials)   *   * If a developer want to add just JS and/or CSS in head, he/she can just use the action pexlechris_adminer_head.   * See plugin's FAQs, for more.   *   * @since 2.1.0   *   * @link https://www.adminer.org/en/plugins/#use Documentation URL.   * @link https://www.adminer.org/en/plugins/ Adminer' plugins Documentation URL.   * @link https://www.adminer.org/en/extension/ Adminer' extensions Documentation URL.   */ 

The answer in this question is complicated.
The best solution is to create a Database User with the appropriate privileges.
Maybe you can do it also with WordPress actions.
Read more in this support ticket.

By default, you haven’t access to any database other than the site’s database. In order to enable access, you need to add the following line code define('PEXLECHRIS_ADMINER_HAVE_ACCESS_ONLY_IN_WP_DB', false); in the wp-config.php file.

Replace phpMyAdmin with Adminer and you will get a tidier user interface, better support for MySQL features, higher performance and more security. See detailed comparison.
Adminer development priorities are: 1. Security, 2. User experience, 3. Performance, 4. Feature set, 5. Size.