Page titles are wrapped in a span tag
This is probably not the case for all pages? I think what you see is the rendered result of an entity field like for example this node field template:
field--node--title.html.twig:
&lt;span{{ attributes }}&gt;
  {%- for item in items -%}
    {{ item.content }}
  {%- endfor -%}
&lt;/span&gt;

In other cases when the title is not bubbled up from the rendered main content and it is taken from the route definition there shouldn't be a span tag unless there is a title callback placing such a tag.