I have a question about data variables.. why can I not use a data variable that I created in the body in links?

I created a data variable called registrationLink and set it as string and set the value as the final destination link that I want the users to divert to (this is an external link)

I have a landing with multiple buttons and I want to bind the url to this registration link so that when I update the registrationLink once, it updates everywhere..

Obviously I am doing something wrong / or I don't really understand the purpose of data variables.

How can I achieve this, where I update the link once and it gets updated everywhere?

It's on a single landing page within the body

I verified the DNS and made sure the changes have propagated.

I am using Cloudflare - and I get a notice stating something about CNAME flattening?
CNAME records normally can not be on the zone apex. We use CNAME flattening to make it possible. - Learn more (https://developers.cloudflare.com/dns/cname-flattening/)

Should I wait longer to ensure the DNS records have updated / propagated?