Applying trim to paragraph value

I have the following Paragraph template which displays a heading with a trailing orange dot. The field itself is a normal text field in Drupal. For some reason, there is a trailing space after the heading, which leads to a space between the heading and the dot. I want to remove it (and |trim is the answer), but when I add trim to the below variable I get a PHP warning saying parameter 1 should be a string, not an array.

How do I then get the absolute value of the paragraph value?

{% block paragraph %}
  <div{{ attributes.addClass(classes) }}>
    {% block content %}
      <h1>{{ content.field_heading_h1 }}<i class="orange">.</i></h1>
    {% endblock %}
  </div>
{% endblock paragraph %}

The following gives the PHP error:

{% block paragraph %}
  <div{{ attributes.addClass(classes) }}>
    {% block content %}
      <h1>{{ content.field_heading_h1|trim }}<i class="orange">.</i></h1>
    {% endblock %}
  </div>
{% endblock paragraph %}

Warning: trim() expects parameter 1 to be string, array given in twig_trim_filter()

As the warning states, content.field_heading_h1 is a (render)-array

you could check it´s structure using {{ kint(content.field_heading_h1) }} (devel-module)

probably you can get the plain text value and trim it with:

{{ content.field_heading_h1.value|trim }}

or

{{ content.field_heading_h1.0|trim }}

refering to How do I get the raw field value in a twig template?

thats just one way to do "operation on symptoms" but the actual question to ask is why there is a whitespace and is there a way to prevent that already in the form that saves it