Print a list of checked form options in TWIG
Iterate over the form options, returning the # value of each item:

{% for choice in form.filter['#value'] %}

Then Print out the title value of each one of those options:

{{ form.filter[choice]['#title'] }}

All together it looks like this:

{% for choice in form.filter['#value'] %} {# Find each checked option #}
  {{ form.filter[choice]['#title'] }} {# Print the Title #}
{% endfor %}