Thymeleaf th:text – Put a text without removing HTML structures

I faced the same problem. The answer is th:inline="text"

This should solve your issue

<h1 th:inline="text" >
   [[${header.title}]]
   <small th:text="${header.subtitle}">Subtitle</small>
</h1>

or you can also use th:remove="tag"

<h1>
    <span th:text="${header.title}" th:remove="tag">title</span>
    <small th:text="${header.subtitle}" >Subtitle</small>
</h1>