checkbox with get_option not working

Full code to add settings page with checkbox option. You don’t need loops and something else. WordPress will make everything for you. Get more info in Codex

function wpse_319648_render_popup() {
    $options = get_option('wpse_319648_checkbox');
    $default = isset($options['popup']) ? $options['popup'] : 0;

    printf(
        '<input type="checkbox" name="%1$s[popup]" value="1" %2$s>',
        'wpse_319648_checkbox',
        checked($default, 1, false)
    );
}

function wpse_319648_settings_page() {
    echo '<form class="wrap" action="options.php" method="post">';
    settings_fields('wpse-319648-settings');
    do_settings_sections('wpse-319648-settings');
    submit_button();
    echo '</form>';
}

add_action('admin_init', function() {
    register_setting('wpse-319648-settings', 'wpse_319648_checkbox');

     add_settings_section(
        'wpse-319648-section',
        __('Settings', 'theme'),
        [],
        'wpse-319648-settings'
    );

    add_settings_field(
        'popup',
        __('Show popup', 'theme'),
        'wpse_319648_render_popup',
        'wpse-319648-settings',
        'wpse-319648-section'
    );
});

add_action('admin_menu', function() {
    add_submenu_page('options-general.php',
        __('Options', 'theme'),
        __('Options', 'theme'),
        'manage_options',
        'my-page',
        'wpse_319648_settings_page'
    );
});

Hope it helps.