Hello,
Thank you for contacting Rank Math and bringing your concern to our attention. I’m sorry for any inconvenience this issue may have caused you.
Rank Math has an option to remove the category base of your products. Please ensure that this option is disabled in WordPress Dashboard > Rank Math > General Settings > WooCommerce.

If the issue persits, could you also share some URL/s or record a video screencast using a tool like Loom showing the issue and edit the first post on this ticket in the designated Sensitive Data section?

It is completely secure, and only our support staff has access to that section.
I hope that helps. Thank you, and looking forward to your update.
Hello,
My settings are correct.
I have updated the sensitive data as requested.
Conclusion of my current problem is:
Rankmath uses the last-created category instead of the primary category for it’s permalinks and canonical URL’s.
Can this be changed? Can you please check further?
regards,
Marco
Thank you.
Hello,
Rank math automatically generates the product slug/permalink from the category set as primary category. I couldn’t replicate the issue with using the last category added.
Would you please check this screencast: https://i.rankmath.com/iOowqU and let me know if this is not the same case on your end?
If you do have an issue on the same still, or this doesn’t cover your issue, please do create a screencast from your end using https://www.loom.com and share in the sensitive section.
Looking forward to helping you
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.