Links to cross-origin destinations are unsafe

what happend if your links go to a https link ( you can have inserted both variants – but take the https one please)

it that does not bring any success you can try this here (and play a bit what you want) in child-theme functions.php

What does the code do: every link that do not fit with your domain url (internal links) get the target blank ( you can get rid of that line) and will get the rel you like.

PS : i would advice you to use noreferrer on that:
read here: https://developers.google.com/web/tools/lighthouse/audits/noopener

rel=”noreferrer” attribute has the same effect, but also prevents the Referer header from being sent to the new page. See Link type “noreferrer”.

to avoid those things from internal links ( your domain) and from e-mail (and maybe encrpyted one) and telephone links – this could be the code to use:

add_action('wp_footer', 'open_external_links_in_newtab');
function open_external_links_in_newtab(){
?>
<script type="text/javascript">
(function($) {
  var domainUrl = window.location.origin;
  $('a').not('a[href*="'+ domainUrl +'"], a[href*="mailto:"], a[href*="tel:"], a[href*="javascript:;"] ').attr({
    'target':'_blank',
    'rel': 'nofollow noreferrer',
  })
})(jQuery);
</script>
<?php
}