Vendor/Module/view/frontend/layout/checkout_index_index.xml
<?xml version="1.0"?>
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" layout="checkout" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
<body>
<referenceBlock name="checkout.root">
<arguments>
<argument name="jsLayout" xsi:type="array">
<item name="components" xsi:type="array">
<item name="checkout" xsi:type="array">
<item name="children" xsi:type="array">
<item name="steps" xsi:type="array">
<item name="children" xsi:type="array">
<item name="shipping-step" xsi:type="array">
<item name="children" xsi:type="array">
<item name="shippingAddress" xsi:type="array">
<item name="children" xsi:type="array">
<item name="shipping-address-fieldset" xsi:type="array">
<item name="children" xsi:type="array">
<item name="firstname" xsi:type="array">
<item name="validation" xsi:type="array">
<item name="min_text_length" xsi:type="number">1</item>
<item name="max_text_length" xsi:type="number">30</item>
<item name="required-entry" xsi:type="boolean">true</item>
<item name="max-words" xsi:type="number">4</item>
</item>
</item>
<item name="lastname" xsi:type="array">
<item name="validation" xsi:type="array">
<item name="min_text_length" xsi:type="number">1</item>
<item name="max_text_length" xsi:type="number">30</item>
<item name="required-entry" xsi:type="boolean">true</item>
<item name="max-words" xsi:type="number">4</item>
</item>
</item>
</item>
</item>
</item>
</item>
</item>
</item>
</item>
</item>
</item>
</item>
</item>
</argument>
</arguments>
</referenceBlock>
</body>
</page>
vendor/magento/module-customer/view/frontend/templates/widget/name.phtml
and need to put maxlength property there.