How do I confirm that the ref is on all links

If External Links is working it should add the attribute data-wpel-link="external" to all external links. If you don’t see that and the External Links settings are enabled then it might be a cache issue. Try clearing any cache plugin/service you have active.

I cleared the caches of all pages. I then clicked a link and this is the URL d631-ttd/p-110186P2?pid=P00097499&mcid=42383&medium=widget&widgetPreview=false&widget_ref=W-54289f6d-f12a-47c8-be24-194a7cb97b39

Is there a step after I have selected all the rules for it to “run” against all active pages?

That does not look like a valid URL. Can you give me a link to the page on your website where WP External Links should be working?

https://youngatheartdeals.com/welcome-to-young-at-heart-deals/destinations/mexico/riviera-maya-excursions-2/

OK, now I see the issue. That bottom section of the page from Viator is loaded via JavaScript after page load. Unfortunately WP External Links can’t change those links as it runs on the server side and can only affect links that are in the pages before they are sent to the client ??

Is there a way to manually add the rel attribute within the code I am using on the website for the Viator widget?

It seems Viator isn’t the only one. https://www.bahia-principe.com/en/?utm_campaign=always-on_USA&n_o_aut_tc=345715318&cjevent=f0fb87a5f43911ed823400ad0a1cb827&utm_content=100756916&utm_term=&utm_source=cjaffiliate&utm_medium=affiliates&cjdata=MXxOfDB8WXww&dclid=CLGunf7y-v4CFca2wAodGJoC1w is a link from this advertiser, on this page: https://youngatheartdeals.com/welcome-to-young-at-heart-deals/destinations/mexico/all-inclusive-resorts/

I don’t see them on this page with non-Viator links, either…https://youngatheartdeals.com/welcome-to-young-at-heart-deals/destinations/dominican-republic/

On https://youngatheartdeals.com/welcome-to-young-at-heart-deals/destinations/mexico/riviera-maya-excursions-2/ you can see that the links higher in the page like Jungle Tour and Snorkeling are modified by WP External Links.

For any links that are added to the page via JavaScript you will need to either modify that JavaScript, if you have access to it or write some extra JavaScript code to update them after the all the links are added to the page. That most likely requires custom JavaScript code so I can’t point you to anything that can help out of the box ??