What im trying to achieve is instead of using the default wordpress settings option to disable registrations (Anyone can register). I want to leave this default option enabled but disable buddypress registration using page redirection

when user tries to access (sign-up) page redirect the user to (coming-soon) page

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' ); 

Hi Brajesh

This is the improved code, there are no more issues

 <?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() {
    if ( ! function_exists( 'bp_is_active' ) ) {
        return;
    }
    register_setting( 'buddypress', 'bp-disable-site-registration', 'custom_bp_sanitize_registration_status' );
    register_setting( 'buddypress', 'bp-disable-site-registration-redirection-url', 'custom_bp_sanitize_redirection_url' );
    register_setting( 'buddypress', 'bp-close-registration-at-users', 'custom_bp_sanitize_user_registration_count' );
}
add_action( 'admin_init', 'custom_bp_register_settings' );

// add sanitization function
function custom_bp_sanitize_registration_status( $status ) {
    $allowed_values = array( 'open', 'closed' );
    if ( ! in_array( $status, $allowed_values ) ) {
        $status = 'open';
    }
    return $status;
}

function custom_bp_sanitize_redirection_url( $url ) {
    return wp_kses_post( $url );
}

function custom_bp_sanitize_user_registration_count( $count ) {
    return absint( $count );
}

// Add the new setting to the BuddyPress options page
function custom_bp_add_settings_field() {
    if ( ! function_exists( 'bp_is_active' ) ) {
        return;
    }
        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( 
        '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', home_url() );
    ?>
    <input type="text" name="bp-disable-site-registration-redirection-url" id="bp-disable-site-registration-redirection-url" value="<?php echo esc_attr( $value ); ?>" required/>
    <?php
}

// Output the HTML for the close registration at users field
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 ); ?>" required/>
    <p class="description"><?php _e( 'Enter the maximum number of users allowed to register on the site. Leave it empty or set to 0 for no limit.', 'buddypress' ); ?></p>
    <?php
}

// Check if registration is open or closed
function custom_bp_redirect_registration() {
    $total_users = count_users();
    $total_users = $total_users['total_users'];
    $registration_status = get_option( 'bp-disable-site-registration', 'open' );
    $limit_user_registration_count = get_option( 'bp-close-registration-at-users' );
    if ( bp_is_register_page() && $registration_status === 'closed' && ( (empty($limit_user_registration_count) || $limit_user_registration_count == 0) || $total_users >= $limit_user_registration_count ) ) { 
        wp_redirect( get_option( 'bp-disable-site-registration-redirection-url' ) );
        exit;
    }
}
add_action( 'bp_screens', 'custom_bp_redirect_registration' );