Listing all users by their avatars in wordpress

• You have to retrieve all users with this get_users() and loop through them.
• Then you have to get the avatar URL using a current user id with this get_avatar_url().

$users = get_users( array( 'fields' => array( 'ID' ) ) );

// Array of stdClass objects.
foreach ( $users as $user ) :

    $avatar = get_avatar_url( $user->ID );
    // If you want to retrieve specifc size image.
    // $avatar = get_avatar_url( $user->ID, array( 'size' => '300') );
        
    if ( $avatar ) :
      echo '<img src=" ' . esc_url( $avatar ) . ' " />';
    endif;

endforeach;

You can jump start by using following example. Here I'll be listing users and loop through them to display avatar and display name.

<?php
$blogusers = get_users();
// Array of WP_User objects.
foreach ( $blogusers as $user ) {
    /* Here passing user email and avater size */
    echo get_avatar( $user->user_email , 96 );
    echo '<span>' . esc_html( $user->display_name ) . '</span>';
}

Read more about

1. get_users()
2. get_avatar()