Sorry For stomping on this thread, but I would like to point out that your dashboard needs to be setup in advanced view to enable the ACF module, but I think this is active by default.
Now, I have a further question. What role does ACF play in the SEO analysis? I do not see any mention of this ACF within that MathRank SEO Analysis tab. As ACF is dynamic and every website is different, what content is getting analyzed? Are FOCUS keywords expected here? Looking for insight on ACF is analyzed against SEO metrics.
The ACF module is usually enabled automatically if your site already has an existing ACF plugin which Rank math is able to detect.
Some users prefer to use Custom fields to add content to their pages and posts. By default, Rank math is only able to analyse content added through the WordPress editor and a number of builders. Enabling the ACF module allows Rank math to be able to include the custom fields in analysis and therefore giving the post or page editor more accurate references and page/post score.
Hope that helps. If you have any further question(s), please let us know. Thank you.