Hello,
We apologize for the issue you are facing. Currently, Rank Math allows you to set a primary taxonomy for products, but it does not explicitly mention the ability to set a primary category for native categories or custom taxonomies created with ACF.
For custom taxonomies, you may need to check if they are supported by Rank Math for primary term settings. If you have further questions or need specific guidance on this, we recommend replying to this ticket, and a human agent from the Rank Math Support team will assist you further.
Thank you for raising this concern!
Hello,
Thank you for contacting Rank Math support.
Yes, very much so. The process is the same as with default post types. Navigate to Rank Math > Title & Meta > [Post Type] > Primary Taxonomy and set the primary taxonomy for the post type.

Then you’d be able to select a primary taxonomy for the individual custom post type, as you would other post types

We hope this helps clarify the issue. Please let us know if you have any other questions or concerns.
Hello,
Since we did not hear back from you for 15 days, we are assuming that you found the solution. We are closing this support ticket.
If you still need assistance or any other help, please feel free to open a new support ticket, and we will be more than happy to assist.
Thank you.