Hello,
Thank you for contacting Rank Math support, and sorry for any inconvenience that might have been caused due to that.
Can you please check if you have selected “Categories” as your Primary Taxonomy in Rank Math > Titles & Meta > Post Type?

If you already did and the issue persists, we might need to take a closer look at the settings. Please edit the first post on this ticket and include your WordPress login in the designated Sensitive Data section.
Please do take a complete backup of your website before sharing the information with us.

It is completely secure and only our support staff has access to that section. If you want, you can use the below plugin to generate a temporary login URL to your website and share that with us instead:
https://wordpress.org/plugins/temporary-login-without-password/
You can use the above plugin in conjunction with the WP Security Audit Log to monitor what changes our staff might make on your website (if any):
https://wordpress.org/plugins/wp-security-audit-log/
We really look forward to helping you.
I have already selected Primary Taxonomy from Titles & Meta > Post Type. The Problem is still there. I have spined a fresh docker installation with latest WordPress and Rankmath and nothing else and the problem is still there.
I can’t provide you with login data, as this is against the security policy in my agency.
This feature is very important for use, as we have a lot of taxonomies on some projects and we can’t use the plugin at all…
Hello,
It seems to be working fine on our end using the latest version of Rank Math.

Please select/check at least 2 categories in your categories list and the primary taxonomy should be shown below.
Let us know how this goes.
Thank you.