https://endurtech.com/replace-wordpress-admin-bar-welcome-text-howdy/

endurtech-replace-howdy-wordpress-admin-bar.php

<?php

// Replace WordPress Admin Bar Welcome Message with Custom Text
// Replaces the default 'Howdy' welcome text at the top right next to the logged in username with text of your own choosing.
// https://endurtech.com/replace-wordpress-admin-bar-welcome-text-howdy/

add_action( 'wp_before_admin_bar_render', 'replace_howdy_text' );
function replace_howdy_text()
{
    global $wp_admin_bar;
    $my_account = $wp_admin_bar->get_node( 'my-account' );
    if ( ! $my_account || ! isset( $my_account->title ) )
    {
        return;
    }
    $welcome_text = 'Hello,'; // Replace Hello with your custom Welcome text message.
    $new_title = str_replace( 'Howdy,', $welcome_text, $my_account->title );
    $wp_admin_bar->add_node( array(
        'id'     => 'my-account',
        'title'  => $new_title,
    ) );
}

?>