public function afterProcess (
    MagentoCheckoutBlockCheckoutLayoutProcessor $subject,
    array  $jsLayout
) {
    $jsLayout['components']['checkout']['children']['steps']['children']['shipping-step']['children']
    ['shippingAddress']['children']['shippingAdditional'] = [
        'component' => 'uiComponent',
        'displayArea' => 'shippingAdditional',
        'children' => [
            'terminal' => [
                'component' => 'Vendor_Module/js/methods/method',
                'config' => [
                    'customScope' => 'shippingAddress',
                    'template' => 'ui/form/field',
                    'elementTmpl' => 'Vendor_Module/method',
                    'options' => [],
                ],
                'dataScope' => 'shippingAddress.method_terminal',
                'label' => '',
                'provider' => 'checkoutProvider',
                'visible' => true,
                'validation' => [ 'select-terminal-required' => true ],
                'sortOrder' => 200,
            ]
        ],
    ];
    return $jsLayout;
}

<div data-bind="visible: selectedMethod () == 'vendor_terminal'">
 <label data-bind="i18n: 'Select'"></label>
 <select name="vendor-terminal" class="select-terminal-required" id="terminal-list" data-bind="html: getTerminalList ()">
 </select>
</div>

var config = {
    config: {
        mixins: {
            'Magento_Ui/js/lib/validation/validator': {
                'Vendor_Module/js/validation-mixin': true
            },
    }
}

define([
    'jquery',
    'Magento_Checkout/js/model/quote',
    'Magento_Ui/js/lib/validation/utils'
], function ($, quote, utils) {
    "use strict";
    return function ( validator ) {
        validator.addRule ( 'select-terminal-required', function () {
            var method = quote.shippingMethod();
            var validation = method.method_code === 'vendor_terminal' && utils.isEmpty($( '.select-terminal-required' ).val ());
            return !validation;
        }, $.mage.__( 'Please select terminal.' ) );

        return validator;
    }
});