Hello,
Thank you for contacting Rank Math and sorry for any inconvenience that might have been caused due to that.
Rank math understands pages/posts with user-defined canonical as duplicate pages, and therefore they are not added to the sitemap.
You will need to remove the custom canonical to have your page added to the sitemap.
I hope this resolves your issue.
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.