Hi Brajesh

The code worked, it has been further improved to limit based of membership count and work only on bp_is_register_page() can you please review it

 <?php
/*
* Plugin Name: BuddyPress Registration Control
* Description: Allows administrators to enable or disable user registration and select a URL to redirect to when registration is disabled.
* Version: 1.0
*/

// Register the new setting in the BuddyPress options group
function custom_bp_register_settings() {
    register_setting( 'buddypress', 'bp-disable-site-registration', 'sanitize_text_field' );
    register_setting( 'buddypress', 'bp-disable-site-registration-redirection-url', 'sanitize_text_field' );
    register_setting( 'buddypress', 'bp-close-registration-at-users', 'intval' ); // added this line
}
add_action( 'bp_register_admin_settings', 'custom_bp_register_settings' );

// Add the new setting to the BuddyPress options page
function custom_bp_add_settings_field() {
    add_settings_field(
        'bp-disable-site-registration',
        __( 'Registration', 'buddypress' ),
        'custom_bp_settings_field_html',
        'buddypress',
        'bp_main',
        array(
            'label_for' => 'bp-disable-site-registration',
        )
    );
    add_settings_field(
        'bp-disable-site-registration-redirection-url',
        __( 'Redirection URL', 'buddypress' ),
        'custom_bp_settings_redirection_url_html',
        'buddypress',
        'bp_main',
        array(
            'label_for' => 'bp-disable-site-registration-redirection-url',
        )
    );
    add_settings_field( // added this block
        'bp-close-registration-at-users',
        __( 'Limit User Registration Count', 'buddypress' ),
        'custom_bp_close_registration_at_users_html',
        'buddypress',
        'bp_main',
        array(
            'label_for' => 'bp-close-registration-at-users',
        )
    );
}
add_action( 'bp_register_admin_settings', 'custom_bp_add_settings_field', 10, 1 );

// Output the HTML for the setting field
function custom_bp_settings_field_html() {
    $value = get_option( 'bp-disable-site-registration', 'open' );
    ?>
    <select name="bp-disable-site-registration" id="bp-disable-site-registration">
        <option value="open" <?php selected( $value, 'open' ); ?>><?php _e( 'Open', 'buddypress' ); ?></option>
        <option value="closed" <?php selected( $value, 'closed' ); ?>><?php _e( 'Closed', 'buddypress' ); ?></option>
    </select>
    <?php
}

// Output the HTML for the redirection URL field
function custom_bp_settings_redirection_url_html() {
    $value = get_option( 'bp-disable-site-registration-redirection-url' );
    ?>
	<input type="text" name="bp-disable-site-registration-redirection-url" id="bp-disable-site-registration-redirection-url" value="<?php echo esc_attr( $value ); ?>" />
    <?php
}

// Output the HTML for the close registration at users field // added this function
function custom_bp_close_registration_at_users_html() {
    $value = get_option( 'bp-close-registration-at-users' );
    ?>
    <input type="number" name="bp-close-registration-at-users" id="bp-close-registration-at-users" value="<?php echo esc_attr( $value ); ?>" />
    <p class="description"><?php _e( 'Close registration when the total number of users reaches this number.', 'buddypress' ); ?></p>
    <?php
}

// Redirect users if registration is closed
function custom_bp_redirect_registration() {
    $total_users = count_users(); // added this line
    $total_users = $total_users['total_users']; // added this line
    if ( bp_is_register_page() && ( get_option( 'bp-disable-site-registration' ) === 'closed' || $total_users >= get_option( 'bp-close-registration-at-users' ) ) ) { // modified this line
        wp_redirect( get_option( 'bp-disable-site-registration-redirection-url' ) );
        exit;
    }
}
add_action( 'bp_screens', 'custom_bp_redirect_registration' ); 

Thanks this is now resolved

I found this code

 function open_external_links_in_new_tab() {
  echo '<script type="text/javascript">';
  echo 'var links = document.getElementsByTagName("a");';
  echo 'for (var i = 0; i < links.length; i++) {';
  echo 'var link = links[i];';
  echo 'if (link.hostname != window.location.hostname) {';
  echo 'link.target = "_blank";';
  echo '}';
  echo '}';
  echo '</script>';
}
add_action( 'wp_footer', 'open_external_links_in_new_tab' ); 

Kindly review