I'm trying to add no follow attribute to all outbound links in buttons on my website.
All of the links are stored in custom fields on the post type.
Example of the 2 pages where I have links are: hidden link hidden link
I reviewed the other threads on adding nofollow to links, but they were not using the button or associated to a custom field on a different post type. How can I add this simple value to my links?
You can't, I'm afraid, not when you use the Button block.
You can if you use the Fields and Text block and define your own markup for the button, to include the nofollow option.
In this example I took the same markup generated on the front-end by the Block button, and for the href attribute I used the Fields and Views button to insert the shortcode used to generate the URL from a "link" custom field, and then I added a rel="nofollow" attribute to the link. I could similarly add other attributes as required.