The Particle is set to pull in 'raw' text in already which should include HTML formatting.
/particles/swiper.joomla.html.twig line 71
{% if display.text.type != '' %}
<div class="g-swiper-text">
{% set article_text = display.text.type == 'intro' ? article.introtext: article.text %}
{{ article_text|truncate_text(display.text.limit)|raw }}
</div>
{% endif %}
If you set your text length (Articles Display > Text Limit) to more characters than the article... put a bunch of 9s in there... does it work?
I think the 'truncate_text' portion might be tripping it up... if truncate_text can't reach the closing tag of an HTML block I think it'll strip the HTML... so if your Text Limit is less than where the closing </a> tag would fall for example, it'll strip (I think) the <a href="#">....</a> HTML... it's possible if you have <p> tags wrapping your text and it can't reach a closing </p> tag within the Text Limit, it'll strip the HTML...
Run some tests with an article that JUST contains a hyperlink and has an adequate character count set
It's either that or Joomla is stripping the HTML when it's passed to the Particle.