@Qwerty1
I recently completed my medical examination using my Canadian passport, even though I had used my renounced (Previous Nationality) passport when filing my case with NVC.
I confirmed with my attorney that such situations are common. They advised that I should carry both my old, renounced passport and my new Canadian passport. You may also need to provide proof of your other citizenship. In my specific situation, my old citizenship was renounced.
I hope this information is helpful.